New build - need help with CV40 carb set up please

[Adam76]

Hey guys,
Just completed my '02 Fatboy build, 95ci big bore, fresh set of '09 heads, CR575 cams, DTT ignition and basic supporting mods. Carb was rebuilt with a full rebuild kit

I started it today for its first heat cycle with the choke (enricher) out all the way. Starts and runs...  But as soon as I start to push the choke knob back in and try to hold the throttle slightly open, big puffs of black smoke come out the exhaust and it just comletely dies, even if I give it more throttle....

Runs smoothly with choke on full
Runs horribly, black smoke then stalls when the choke is pushed in.


DTT  set to  #2 #3 #0  for first 3 dials
46 pilot jet
195 main jet
CV Performance needle
Float level (angle) checked before reassebly
Tried a/f mixture screw at 1 3/4 turns out to 2 1/2 turns out - no improvement at any setting.

Any help would be appreciated because I need to get it running well enough to do a break in run.
Thanks

[Don D]

First look at the plugs. Then check compression.

[turboprop]

Hey guys,
Just completed my '02 Fatboy build, 95ci big bore, fresh set of '09 heads, CR575 cams, DTT ignition and basic supporting mods. Carb was rebuilt with a full rebuild kit

I started it today for its first heat cycle with the choke (enricher) out all the way. Starts and runs...  But as soon as I start to push the choke knob back in and try to hold the throttle slightly open, big puffs of black smoke come out the exhaust and it just comletely dies, even if I give it more throttle. It simply will not run without choke on full.

DTT  set to  #2 #3 #0  for first 3 dials
46 pilot jet
195 main jet
CV Performance needle
Float level (angle) checked before reassebly
Tried a/f mixture screw at 1 3/4 turns out to 2 1/2 turns out - no improvement at any setting.

Any help would be appreciated because I need to get it running well enough to do a break in run.
Thanks

The symptoms your bike is exhibiting is not attributable to the jetting package or the position of the idle mixture screw. I suspect an electrical issue.

[Adam76]

First look at the plugs. Then check compression.

Thanks will do. I don't have the compression testing tool, but I can try and get hold of one.

Do you think the compression may be too low or too high?

[Adam76]

Hey guys,
Just completed my '02 Fatboy build, 95ci big bore, fresh set of '09 heads, CR575 cams, DTT ignition and basic supporting mods. Carb was rebuilt with a full rebuild kit

I started it today for its first heat cycle with the choke (enricher) out all the way. Starts and runs...  But as soon as I start to push the choke knob back in and try to hold the throttle slightly open, big puffs of black smoke come out the exhaust and it just comletely dies, even if I give it more throttle. It simply will not run without choke on full.

DTT  set to  #2 #3 #0  for first 3 dials
46 pilot jet
195 main jet
CV Performance needle
Float level (angle) checked before reassebly
Tried a/f mixture screw at 1 3/4 turns out to 2 1/2 turns out - no improvement at any setting.

Any help would be appreciated because I need to get it running well enough to do a break in run.
Thanks

The symptoms your bike is exhibiting is not attributable to the jetting package or the position of the idle mixture screw. I suspect an electrical issue.

Ok thanks, where do you suggest I start looking for electrical issues?

[turboprop]

Come on, impossible via internet. You are pretty thorough. I would start with checking all of the grounds, voltage drop at the starter and the power input into the module and at the coil. Would also check resistance from assorted places on the the bike to the negative terminal.

It could be a vacuum leak but I doubt it. I had a similar experience last summer. I had an issue with the clutch in one of my FXRs, ended u pulling the inner primary case and rebuilding a bunch of stuff over a few months. When I fired up the bike it ran like "Potty mouth", the AFR was all wrong, like way out of wack. Would only run with the choke and would not take throttle. What was it, I failed to connect the chassis to drive train ground strap. On an FXR it is under the transmission between the frame and the trans case. I simply missed it because the build took so long. The engine had all the symptoms of a fuel issue, the onboard AFR even confirmed it was extremely lean. Once that ground was restored everything went back to normal. Learning definitely occurred in my garage that week.

You will find it.

[Adam76]

Ok thanks Turbo, my symptoms match exactly what you've described...
electrical issues are my least favorite problems 😁 but definitely appreciate your advice.

I know that I did take the starter motor out to replace the starter clutch during the build - maybe I did something wrong there?

Cheers

[Adam76]

Any chance it could be a damaged / broken / pinched diaphragm in the carb? That was the only thing not replaced during the carb rebuild??

Cheers

[turboprop]

Any chance it could be a damaged / broken / pinched diaphragm in the carb? That was the only thing not replaced during the carb rebuild??

Cheers

I doubt it. But now that you said it, you aren't going to sleep until you check it.

[Adam76]

Yeah, because if it runs "smoothly" on full choke, then it can't be the diaphragm, right? Otherwise it wouldn't run properly choke or no choke... is that right?
Thanks

[turboprop]

You know you want to do it.

[Adam76]

Double post

[Adam76]

With the bike off and ignition off,  when I twist the throttle fuel is squirted in, but the slide does NOT move up at all.... is this normal?
Thanks

[Adam76]

I'm no expert on reading plugs but this rear cylinder plug doesn't look too good.

[Hossamania]

With the bike off and ignition off,  when I twist the throttle fuel is squirted in, but the slide does NOT move up at all.... is this normal?
Thanks

Yes, the slide is vacuum operated, the bike must be running for it to operate. Does it move with the throttle while running?
If you reach in and lift it (not running) it should move easily, but you should hear or feel a little vacuum resistance, or air pump effect. A damaged diaphragm usually causes a lean condition, not a rich condition.

[Hossamania]

What settings are you using on the DTT?  5/5 is a good start initial timing and slope, setting 1 for multispark. 6100 rpm limit, setting 1 for that. Don't worry it being so high, you're not going there. Yet.
As turboprop said, check your wiring and grounds again.
Was the float properly set in the carb?
A compression test is a good idea to at least eliminate that as an issue.
Make sure the battery has a full charge.
Make sure your MAP sensor on the intake manifold is plugged in.

[turboprop]

With the bike off and ignition off,  when I twist the throttle fuel is squirted in, but the slide does NOT move up at all.... is this normal?
Thanks

Yes.

[Don D]

I would pull the plugs, ground one, the metal body, connected to wire and spin it over. What does the spark look like? Fat and red? Thin and blue? Autoshop 101 I know not sexy but it would save some time maybe.

[hrdtail78]

Tried a/f mixture screw at 1 3/4 turns out to 2 1/2 turns out - no improvement at any setting.

Any help would be appreciated because I need to get it running well enough to do a break in run.
Thanks

If turning your mixture screw with no change on a fully warmed engine.  It's a good sign the pilot isn't letting in enough fuel to maintain idle. 

[Adam76]

What settings are you using on the DTT?  5/5 is a good start initial timing and slope, setting 1 for multispark. 6100 rpm limit, setting 1 for that. Don't worry it being so high, you're not going there. Yet.
As turboprop said, check your wiring and grounds again.
Was the float properly set in the carb?
A compression test is a good idea to at least eliminate that as an issue.
Make sure the battery has a full charge.
Make sure your MAP sensor on the intake manifold is plugged in.

Thanks Hoss, I'll adjust the ignition settings.
When I rebuilt the carb I thought I did a thorough job of checking the float was properly angled.... I didn't adjust it. The battery also was checked and has good voltage and CCA.

I'll have another look at the MAP sensor on top of the intake manifold.

Cheers

[Adam76]

Tried a/f mixture screw at 1 3/4 turns out to 2 1/2 turns out - no improvement at any setting.

Any help would be appreciated because I need to get it running well enough to do a break in run.
Thanks

If turning your mixture screw with no change on a fully warmed engine.  It's a good sign the pilot isn't letting in enough fuel to maintain idle.

Hey hardtail, thanks for the reply. The engine has only run for max of 30 secs because it will only run on full choke - so no where near reaching fully warm operating temp.
Cheers

[Adam76]

I would pull the plugs, ground one, the metal body, connected to wire and spin it over. What does the spark look like? Fat and red? Thin and blue? Autoshop 101 I know not sexy but it would save some time maybe.

Thanks, I'll give this a go. Electrical stuff is not my forte 😁

Can you elaborate on exactly what I do for this test ? Pull both plugs? Ground only one, what do I do with the other one?

Thanks, sorry for the stupid questions.
Cheers

[Adam76]

I had a similar experience last summer. I had an issue with the clutch in one of my FXRs, ended u pulling the inner primary case and rebuilding a bunch of stuff over a few months. When I fired up the bike it ran like "Potty mouth" the AFR was all wrong, like way out of wack. Would only run with the choke and would not take throttle. What was it, I failed to connect the chassis to drive train ground strap. On an FXR it is under the transmission between the frame and the trans case. I simply missed it because the build took so long. The engine had all the symptoms of a fuel issue, the onboard AFR even confirmed it was extremely lean. Once that ground was restored everything went back to normal. Learning definitely occurred in my garage that week.

You will find it.

Yeah, that's sounds exactly like what's going on. I've checked the ground from the neg battery to the frame and the ground that goes under the oil tank attached to the starter. All seem good... just found out it's a 5 week wait to get a booking with the top two indy harley techs in my city. What is the ground strap you're taking about with your fxr? Maybe I'm still missing something.

[turboprop]

I had a similar experience last summer. I had an issue with the clutch in one of my FXRs, ended u pulling the inner primary case and rebuilding a bunch of stuff over a few months. When I fired up the bike it ran like "Potty mouth" the AFR was all wrong, like way out of wack. Would only run with the choke and would not take throttle. What was it, I failed to connect the chassis to drive train ground strap. On an FXR it is under the transmission between the frame and the trans case. I simply missed it because the build took so long. The engine had all the symptoms of a fuel issue, the onboard AFR even confirmed it was extremely lean. Once that ground was restored everything went back to normal. Learning definitely occurred in my garage that week.

You will find it.

Yeah, that's sounds exactly like what's going on. I've checked the ground from the neg battery to the frame and the ground that goes under the oil tank attached to the starter. All seem good... just found out it's a 5 week wait to get a booking with the top two indy harley techs in my city. What is the ground strap you're taking about with your fxr? Maybe I'm still missing something.

On an FXR there is a large, braided ground strap that attaches to the crossover on the frame and to the transmission. There is a 5/16" bolt that is accessible from the right side of the bike that goes through the transmission case and threads into the inner primary case. That is the point of attachment on the drive train. The rear cross member on an FXR also serves as a mount for the kick stand stop. The ground strap terminal is sandwiched between two internal and external star washers and is attached to the rear crossmember with a 5/16" bolt.

This is a brief explanation why this ground affected the ignition system but allowed the engine to easily crank over. In item form, the FXR has a cable that goes directly from the negative terminal on the battery to a bonding point on the inner primary case, near the starter. The ignition module is grounded to the frame. There are a bunch of wires grounded to the frame, but without that cable between the frame and the drive train the path to the negative terminal is gone. In my case, the bolt that attached the cable between the frame and the transmission was just sort of sitting in the hole, not even threaded in. It had just enough contact to allow the starter relay to apply power to the starter. It also provided just enough to get the engine to run, but was sporadic and when throttle was applied the engine would die. Plugs looked rich, AFR gauge showed lean, etc. All indicators were that it was a fuel problem. I foolishly chased it.

Good luck.

[Adam76]

Thanks turbo,
I checked all my grounding wires that I could find - all seemed good except the one coming from the voltage regulator that grounds itself to the rectifier mounting bracket.

But I don't know that was the issue.

Thanks again for your help.