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David's Carbie XX ~ FPro Mods ~ Help Required, Gents!

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5.9K views 24 replies 7 participants last post by  TigreST  
#1 ·
Evening Gentlemen.

I have been exchanging emails with a chap over the last week or two. He has been installing Factory Pro kit to his Carbie XX and the bike is running like cr*p under my less-than-expert tutoring.

I'll pass the microphone over to Dave to bring you all up to speed on his scooter, the mods performed and the performance issues that have surfaced.

Experts, step up and sign in please!

:hotsmile:

Gaz.
 
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#3 ·
Thanks Gazza, I have to say I'm a bit stumped and would appreciate some help.

The setup is a '97 carb bird (British Import) with 48k Miles on the clock. Pretty much standard breathing - new (ish) SS headers and a couple of oldish carbon scorpions and a new paper air filter from Jaws. I have just fitted a factory pro ignition advancer (4 degrees) today and have upgraded from my previous dynojet level 1 kit to a factory pro kit as follows:

In the carbs I have previously had a DJ150 main jets, stock 42 pilots, new emulsion tubes and DJ needles clipped 3rd notch from the top and drilled air holes in the lifters to 2.65mm. The bike has been recently run on a dyno to get a before reading (without the ignition advancer). The dyno gave 144hp at the read wheel and about 13.5 A/F mixture above 8000 rev but was very rich at low revs and the started to lean to about 5k revs then went full rich again at 5-6k which corresponded with a flat power spot (which is actually what this is all about).

Today I fitted the FP kit, because of the limited tune (if any) to the engine I used FP 142 main jets on the outer two cylinders and 145 on the middle two. The reason for this was that the kit only came with 2x 142 jets (not sure why) and 4x each of 145, 148, and 150's. I did not touch the pilots. I also changed the DJ needles to the FP supplied ones and fitted the clip to the 2nd from top indent (as recommended) on the needles there is also a shim sitting between this clip and the needle seat which I left in. I removed the DJ springs and refitted the old springs. I am not sure if they are OEM or not as when I originally fitted the DJ kit I found that the needles and jets were already DJ's but the springs were different lengths, The springs that I have put back in measure 112mm in length and were all the same length. I was careful with the fitting and have had these carbs apart so many times that I feel related to them. I set the four idle mixture screws to 2.5 turns out.

When I fired her up it sounded pretty good but a little rough. It has aways run a little rough at idle which seems to get worse as it warms up. I did a carb balance. The bike was burbling away possibly a little worse than usual but responded very well to a few tweaks of throttle so I assume it was all ok.

So wifey decides its a nice day to go for a ride (and it was) so I wacked it back together and headed off into the sunset.. well actually up the nearest long hill and it started to run a bit rough. A got to a straight stretch and opened the throttle and it pulled well to about 4k and then bogged. Dropped the power off and had another go and this time it dropped at least one cylinder. Now at the top of the hill its running pretty rough. Down the other side we go and it now appears to be dropping two cylinders with plenty of backfiring. Eventually the backfiring stops completely and we limp home on two cylinders that appear to be working fairly well. It could of course be something unrelated to the carbs such as an ignition coil but given the amount of tinkering I have done I suspect this is wishful thinking on my part. (Wifey subsequently decided that she would sit on the back of my SP1 for a ride, which by the time we got back she was sorely regretted as the SP1 is not an ideal two up comfort machine).

So here I am pondering my next step. I have noticed a couple of other possibly unrelated but a bit strange things. 1. When the bike is on its side stand it sometimes leaks petrol. I think that it is coming through one of the carburettors as I have seen fuel come out of one of the carb breathers once. This would indicate a sticking float but I cant find one. Also I have previously had some problems with the tank breather becoming blocked but I think I have that sorted now. The 2nd one is that the bike will no longer start in gear with the clutch in - it must be in neutral. I have likely buggered something else for this to happen but thought I'd mention it just in case.

So the first war and peace epistle is complete and I lie here contemplating 25 degrees blue sky's and another weeks holiday before i go back to work wondering where now????
 
#4 ·
I have the FP carb kit also, but have not installed it as I've not changed out the stock exhaust system yet at this point. What I'm about to related is very much commentary for someone who's carbs remain untouched at this point but I offer up for your consideration.

1) The stock jetting from Honda has the #2 and #3 cylinders jetted one size richer then the #1 and #4 cylinders. This I believe is to help with heat generation related to little or no cooling airflow over the middle cylinders. Richer jetting on #2 and #3 will reduce the cylinder temperatures. FP theory is to balance the jetting across all the cylinders for "best power" so provide the odd number (only two) jets to allow one to do this,..you can jet up the #1 and #4 cylinders so there are 142's across the board. I believe (just going from memory here,..which has been wrong before) that the stock factory jetting is 140 on the #1/#4 pair,..and 142 on #2/#3 pair.

2) FP do not drill the slides as DJ recommend with there kits. Plugging the slide holes and redrilling to stock size may be something to consider if for no other reason that it will return you back to a stock baseline starting point for the FP kit install. I believe that DJ drill the slides in a effort to ensure the slides open sooner for both better throttle response or to help the kit get past a flat spot in the transition that often happens when one tampers with the factory settings on CV (vacuum lift) carbs.

3) Springs are not part of the FP kit either,..so I can't comment on where/what to do here. My logic would having me tracking down and ensureing that I was using the stock springs if I was doing the FP kit install.

4) Fuel leakage: The fuel tank uses a vacuum operated shut off valve that only should open when the engine is cranking (pulling vacuum). If fuel is leaking by here this could lead to a carb overflow possibly. The question would then of course be, is the carb float level correct? Is the carb float/s actually floating and working correctly thus shuting off fuel as required? Are the float valves in proper function in a float operating sense...are they seating properly and shutting off the fuel at upper float bowl fuel levels as would be correct?...if not why not? If a float has failed (is sinking in the gas) this could also be an issue to fix. I'm guessing again, but I'm not sure the float levels are adjustable....I think they are not, so if there is a level issue you may have to change the float out completely...but don't quote me on this.

The dropping of the cylinders: Is this due to the fouling of the spark plugs due to a rich condition. Could the rich condition be related to a float bowl fuel level issue as might be happening related in item #4 above?

This has been stated by me before when talking DynoJet. Do not believe that the DJ jet numbers related to the factory jet sizing,..the may not. For the longest time when installing the DJ kit to the older CB-F machines this was a common mistake in thinking. DJ use or did use there own jet sizing numbers that do not relate to stock jet sizing system as used by Keihin. I'd suggest that if you are given a chance that you measure the DJ jet sizes and see if they compare to the Keihin style jet numbers as supplied by FP. If you have a drildex drill bit selection to access you can use these to help size the DJ jetting bores perhaps.

Another classic issue when it comes to jetting trouble is the carb boots or "carb insulators" in Honda parts speak. These are the rubber units that connect the carbs to the cylinder head. Over time and heat cycles they get hard and can crack letting in air where it is not needed or wanted. The removal and re-install of the carb set can cause them to crack and leak, more so with older parts.

Filters: It is noted that the stock filter element seems to be the best for old CB-F CV carb systems. K&N high flow filter seemed to upset the vacuum production and airbox function enough to cause carb and jetting issues. The same may be true of the XX system. The stock filter and stock airbox set up may need to be fully intact to get the most out of the stock carbs.

I have the FP install info saved on site,..if you need it I can attach it to this thread.

I hope this ramblings help some.

Tony
 
#5 ·
Welcome David sorry to read your 'problems' ................... which I'm not going to try to solve since carbies are not my 'area of expertise'!

However
The 2nd one is that the bike will no longer start in gear with the clutch in - it must be in neutral. I have likely buggered something else for this to happen but thought I'd mention it just in case.
Click to expand...
this is generally one of two things both related to the switch that is located under the fluid reservoir.
1. The switch contacts are dirty / the switch has 'died' (unusual)
2. The lever is not being pulled far enough in to the bars to 'break' the switch. Now this can be due to aftermarket levers (some just don't work!). Aftermarket levers that have been adjusted too far. Cables jammed under the bars stopping the lever being pulled right back (heated grips being the usual crims here)

Should be a simple fix, personally I prefer to remove the lever assy from the bar when cleaning up this area, much easier to work on.

EDIT just had one thought on the 'overflow', did it happen on a hot day just after you had fuelled up?

EDIT 2 just read
Gaz said:
Experts, step up and sign in please!
Click to expand...
............... now how do I delete this post :smilebig:
 
H
#6 ·
Perhaps of some help...
Dynojet springs are 4.1" in length, 45 coils, OD of .370" and wire diameter of .020"
Dynojet slide lift hole is drilled with a #37 wire drill which measures 2.65mm (Sorry for going back and forth)
Stock slide lift hole is .059" or 1.5mm
42 pilot and 3 turns out...
Factory pro uses stock springs, stock slide lift holes, generally 145 outer and 148 inner or all 148 mains, e-clip in the 3rd groove with one washer below the clip and a 42 pilot and fuel screws at 3 turns out.
Both kits prefer standard air filter with unmodified air box, snorkles intact, and all ducting in front intact.
Hope that sorts your mixed parts but I think the problem is the carb/carbs is overflowing which should be the first order of business. Also check that the enrichener slide returns fully.
If either 1&4 or 2&3 fouled, check ignition.
If any single or pair (1&2 or 3&4) fouled, check fuel.
Let us know....
Hank
 
#7 ·
Morning All. Thanks for chipping in, Chaps.

Dave. I'd like you to check that you have fuel flow from the tank. I know it sounds simple, but many a XX rider has been caught out with a lack of vacuum provided from the rear of one of the carbs to the vacuum operated petcock under the tank. The symptoms you have describe sound like fuel starvation. The XX will stagger on for a long time on fuel bowl petrol only for ages. Lift the tank and prop it up from the back, just high enough to get you hands in underneath. Make sure the petcock lever is in the 'on' position (sorry, I know this sounds too obvious, but you'd be surprised how many people it catches out...me included...doh) Remove one of the big fat fuel lines off the back of the carb ass'y. Stick this in a jar. Pull the small vacuum line off the back of the (#2?) carb (this line runs to the petcock). Now, suck on the end of this small line (vacuum only, so you won't get petrol in your mouth). Petrol should flow from the big fuel line into the jar.

Now. Another thing to try is to refit all fuel and vacuum lines then pop the fuel filler cap open and try again. If you have a blocked fuel tank breather pipe, this test will bypass the problem.

Have you dropped the petcock off the bottom of the tank and cleaned the fine mesh filter that sits above the petcock?

Have you had a look at the 'plugs? Wet? Black? Have you got spark to each? Remove each one and rest the 'plug body against an earth point on the bike. Crank. Do you see a spark. Test each plug.

Are all spark plug leads well connected? Are the wires from the harness to the back of each coil plugged on securely? These have metal blades inside the rubber caps and it is possible to 'miss' the male connectors on the coils.

Sounds like the problem you have is a very basic one and not related to the 'fine tuning' of the new kit.

As discussed, I run FP150's stock springs stretched to 120mm, OEM 42 pilots, Idle mix at 3 turns out, Jaws HiFlow paper element, FP needles setup as per factory recommendations. Slides drilled to DJ sizing. I found that the slides opened a tad too fast under WOT applications, couldn't be arsed filled and redrilling, so just stretched the springs from 112mm to 120mm to slow them down a bit. Worked perfectly. Excellent throttle response after that.


Here are the DJ Spring and slide hole specs:

DJ Springs
Length 4.1”
# of coils 45
Outer dia. 0.370”
Wire dia. 0.020”
The size of the drill for the slide lift hole is #37 wire size or 2.65mm.
The stock slide lift hole size should be 0.059 or 1.5mm.


Stock Springs and spacer specs:

Outer Dia 0.358"
Wire Dia 0.020"
22 Coils
Lower Washer 0.02" x 0.268" (nearest needle point)
Upper Washer 0.02" 0.233" (on top of clip, between top of clip and black plastic tube)

Check fuel flow and report back.

G.
 
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#9 ·
Pulled all my archive carb type attachments out of the box. Factroy Pro info shown here. FWIW.

Tony
 

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#10 ·
Afternoon All, Many thanks for the advice. I'm halfway there.

Firstly on pulling the bike to bits I noticed one of the primary leads on the left hand coil was so loose that I think it was disconnected so pretty happy that that is the cause of the two cylinder shut-down. I also worked out the that the adjustable clutch lever on position 1 doesn't activate the clutch switch (position 2 is still fine) so that's why I couldn't start it in gear, Vacuum on fuel cock is fine and have petrol all over my garage floor and feet to prove it. Vacuum tube is too short (has come off a couple of times) so now replaced with one about 3 inches longer Gaz. So I may not have finished the carb problems but I certainly have mad progress on other bits.

I have pulled the carbs off again and put FP145's in all four. I have set the idle mixtures to 2.5 turns open and balanced the carbs. Still very burbly with a bit of hunting going on around idle revs. My biggest suspect at the moment is the spring - photo attached (I think it I can work out how). This measures 113.8mm long and has 22 turns which corresponds with Gaz's view of the OEM spring but the ones that I took out that came with the DJ kit are exactly the same except that they are about 2mm longer so I'm confused.

I haven't put it back together yet and so no test ride. I'd also be interested in how you a meant to adjust the idle mixture screws with the engine running. I would need at least another two joints in my arm.

Photo's of:
1. the sunset from my font deck last night
2. the bike although I usually run a double bubble windscreen for touring - just fitted the oem but can't use my radar detector remote laser lights in my eye's technique with it on.

3. Something useful like a close up of the carb spring that is in there.

Many thanks for all your help. Advice on the next steps appreciated.
 
#11 ·
Dave.

1. ++++++1 on the sunset. I also have great pleasure in posting up stunning pics of our En Zed summer to prod the freezing northern scum in the ribs followed by a hearty round of 'nar, nar, nee, nar, nars'. :hotsmile: . We only got to 26 deg today. Brrrrrrrrr. Pass the mulled wine, a warm lusty wench and an electrically heated cod-piece....

2. Red! That's it. I'm not speaking to you any more. Repaint the bike black and all of your problems will disappear ... and you will add 50mph to the top speed....(oh, no, don't mention the war colour of your bike...)

3. That ain't no DJ spring my friend. They have twice the coil turns but use a lighter wire to compensate.

3. Try winding the idle mixture out to the max 4 turns out to cure the rough idle. Also try sealing the top of the air box with silicone sealant. Chop off the end 50mm of a 5mm flat blade screw driver and push on a length of rubber tubing or heat shrink to give you grip. Bingo, the perfect Gaz-Styleee idle mixture adjustment tool[SUP] I have a patent pending ... 'The Short ****er' (c)[/SUP]

4. You have a rough idle, and I am picking a minor surging issue on steady partial throttle opening at cruise? Maxing out the idle mix screw will also help here as this circuit also influences the performance of the engine at higher revs (partial throttle). Ask me how I know....carbs...bless their hairy, sensitive buttocks.

Gaaaaaaaaaaaaaaaaaaaaaaaaazzzzzzzzzzzzzzzzzzzzzzaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa. Yes, lots of beers in the bright sun shine today. Ahhhhhhhhhhhhhh, summmmmmmmmmmmeeeeeeeeeeeeerrrrrrrrrrrrrrr. :poke:
 
#13 ·
...last one before I go make a strong coffee...

Dave, stretch the springs out to 120mm to offset the larger DJ slide hole. Crisper slide response without bogging the engine due to the needles opening too soon on WOT.

Good night, nurse. Zzzzzzzzzzz.
 
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#15 ·
Good thought regarding the body work, but I am not sure the floats are adjustable on the XX? I could be wrong. The can definitely be measured for the correct height, but not adjusted per se. ...I think.
 
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#16 ·
Wow gents! Settings are 3rd notch from the top of the needles, springs stretch to 120mm. 2.65mm vacuum hole. FP145 main jets, Stock pilot jets, new emulsion tubes, Airbox sealed, Boots checked and good on both carb inlets and outlets. 4 turns out on the idle mixture, float heights checks and good, Carbs balanced, runs like a dream. Best its ever run. Managed to get it out this morning and WOT in 6th gear from 3000 revs is smooth as through to loss of license speed. Just wondering if I need to actually set the idle mixtures or just leave them as they are? Thanks to everyone for your contribution and particularly to Gaz for helping me through this one.
Dave.
 
H
#17 ·
I would turn the fuel screws in 1/2 turn and retest...
If it takes the throttle better and runs better, go in another 1/2 turn to 3 turns and retest.
If a change makes it worse, return to the previous setting...
Trial and error....when finally happy, start tracking fuel consumption.
Should be 40mpg+ when cruising.
Glad you are getting it straightened out.
Hank
 
#18 ·
Bravo, Dave! Apart from the mains (mine are FP150s due to worked head and full akra system) you have the exact same settings at my scooter now. What did you do with the spacers above and below the needle clip?

I'm with Hank. Wind the idle screws back in a tad. I'd put a tenner on 3-turns out being perfect. Test with the engine totally warm (1) smooth idle at rest and (2) smooth, non-surging steady throttle cruise at about 50-70kmph in 6th (remember that the idle circuit affects (effects? ...can never remember which one to use...) more than just the idle itself ~ there is an overlap affect (effect?) higher up the rev range before the needles and main jets kick in.
 
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C
#21 ·
you can adjust float height, you just bend the tab that is against the float needle. Should be in the directions. Here is an excerpt.
The majority of jet kits don't require you to adjust the float height; call the manufacturer ahead of time to see if your application may require this adjustment. If so, you'll need a height measurement tool like the one pictured (available from most Honda dealers), or a small ruler with millimeter markings. Make shore the bottom edge of the float bowl is level, and carefully measure the distance from the edge of the float. Don't be a hamfist here; the float mechanism is very delicate. Adjustments are made by carefully bending the float tang (located at the float's pivot point),. either by gently pushing downward the float, or bending the tang manually.


 
C
#22 ·
also keep in mind you may need to drill the slides. When I did the tuning on mine it was a PITA. I actually had to adjust float height along with drilling the slides and had issues with the springs. No engine is exactly the same but after 3 days of dyno tuning she pulls hard and has great dyno numbers! I used to have the 900RR 1000F and 600F1/F2/F3 settings memorized from so much playing around on the dyno!
 
C
#23 ·
idle circuit is up to around 3500 rpm, then your on the pilot circuit until around 7500 then main circuit up till redline if I remember right. You can determine which way to go by using the choke. If your cruising around say 5000 rpm and its surging or stuttering put the choke on, if it gets worse then your already too rich, if it gets better your running to lean. You can use this to help figure out what way you need to go up or down on your main and pilot jets along with adjusting a/f mixture screws. Think you have to drill out the brass cap to do that.
 
#25 ·
Hopefully not putting a fly in the ointment here but.... Although there has been lots of good input it would be extremely wise to remember some of the basic's. cbrbear has made a light go on with me in this respect.

If one considers the typical or classic Honda tune up he may remember that a valve clearance check is next to the front end of the list of things to do prior to investigating or adjusting anything in a "motor induction system" sense. This is only the more critical when it comes to CV carbs (constant velocity) of which the XX is out fitted with as stock gear. If the valve clearance is not correct the ability for the motor to pull vacuum on the intake system will not be correct, therefore any adjustments made to the carbs may/might be in error. In a basic sense this is why carb sync'ing is left to the last item on the list. (jetting changes aside) of the tune up process.

If the history of the machine is an unknown and that may mean the last (or first) valve clearance check in most case for the XX, has not been performed, you may in fact find yourself adjusting the carbs to suit a lack luster valve clearance issue. The root cause of the issue may be valve clearance and we've tuned it out of the equation with carb adjustments/jetting.

Now,..it sound as if your problems are on the way to being (or are) solved...that's a good thing. But...at some point do a valve clearance check to see what the numbers are. Target the loose end of the spec rather then the tight end of the clearance spec would be my advice. When CV carbs rely so much (100%?) on engine vacuum production to function correctly it makes sense to start there to ensure things are good before heading down the road to major rejetting and carb tuning.

I will say it again...sounds like you've met with some or a lot of success....but do pick a moment to do a clearance check. If things are not correct with the valves..you may find yourself back tracking to a new state of carb tune once the valve clearance is set correctly...that's worse case. On the up side, ..you may find that there is more performance potential available that was not being tapped once the valve clearance is set correctly. The task is somewhat involved, yes. But with current info in hand (valve clearance numbers) you can adjust to correct spec's, and thus have some info to look back on the next time the task is due.

FWIW,

Tony
 
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