stovebolt carb with PVC manifold backfiring through carb

shop deals on amazon
Advertise with us
Shop deals on ebay
Classic Goldwings

Help Support Classic Goldwings:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
A

akolleth

Active member
Supporting Member
Joined
Oct 21, 2014
Messages
43
Reaction score
0
Location
Akron, Ohio
Well its been a long frustrating battle now with this bike going single carb. I had to ditch my original carb (motorcraft 5740) because itg started hemorrhaging gas through parts that never should have gas anywhere near them. didn't want to track down the problem becasue frankly I was sick of it at this point. The manifold I am using is the PVC one. With the the old carb I was able to get it running, but it was stuck at a high idle (2800) I could run it all day long at that idle, but I couldn't get it lower. I was working on finding the cause of the idle speed problem when it ate itself.

So I bought one of the stovebolt carbs. Mounted it up, set the throttle cable in a bracket, charged the battery up, and tried to start her up. Now I can't even get it to start. It will crank for a short second then start to rumble for half a second followed by backfiring up once through the carb. rinse and repeat numerous times. I checked the air/fuel mixture screw and its at 1 1/2 turns out. The idle screw is set right too.

I have been reading online and here and it seems like it could be too lean? I tried opening up the air fuel mixture screw and it didn't do anything. Could it be my points? Vacuum leak? It has new spark plugs, and spark plug caps. The fuel is definitely getting there.

any ideas?
 
Those are noted for being too rich. Try gently seating the mixture screw. Choke wide open. Most have better luck with heat added to the stovebolt carb.
 
When points enter into the equation, you have a whole nother aspect of potential problems.

I'd get the ignition up to snuff first thing since backfire out the carb suggests the timing is wrong or possibly cross fire on the wires etc.
I'll say with all the experimenting going rich and extremely lean on the dft I've done, I never once experienced popping out the carb.

Once ignition is good, make certain there are NO vacuum leaks and check your compression is good. A leaking intake valve can cause backfire through carb.
 
[url=https://classicgoldwings.com/forum/viewtopic.php?p=150396#p150396:3ouvt393 said:
dan filipi » Sat Jun 06, 2015 10:38 pm[/url]":3ouvt393]
When points enter into the equation, you have a whole nother aspect of potential problems.

I'd get the ignition up to snuff first thing since backfire out the carb suggests the timing is wrong or possibly cross fire on the wires etc.
I'll say with all the experimenting going rich and extremely lean on the dft I've done, I never once experienced popping out the carb.

Once ignition is good, make certain there are NO vacuum leaks and check your compression is good. A leaking intake valve can cause backfire through carb.
Click to expand...
I missed the ignition being points. That MUST be timed correctly before going any further. Great advice here.
 
hmmmmm seems like leaking air in manifold is number one problem to get right ...if back firing id say manifold is not sealing now good from the backfiring on pvc set up...might be fine just guessing ....to me dft carbs are more likely rich not lean and especially at idle or low rpm ....then as rpm increases they can go lean as the oldwing motor will double the rpm of the car motors they were design for .....meaning flow is greater than the car motors could produce ....

my guess is manifold is leaking air in .....stock intake horns should be tighten first at heads and then the upper part the manifold to get best chance at sealing things
 
hmmmm pluged e choke and backfire happen ....well this did mean taking carb off ....seems gaskets can fail with carb on and off .....dont know much on the pvc set up ....anyway spark is a problem with oldwings also and it dont take much horsing around with other things to make it get compromised ...sorry to here of the trouble .....timing belts should be tensioned good for ignition to time good ...hope things go your way soon ...the pvc manifolds somewhat look a bit hard to deal with ...but this is only a assumption as many have had success and many had trouble as with all set ups ....leaking air seems to be the number 1 problem with the single set ups as carb is high above all mounts and put quite a bit of leverage on set up .....
 
Soo.... I decided to start with the points and timing as a first candidate. I pulled the old points and man were they pitted as all get out. I was hopeful (and still am) that may have been the issue with ignition. I got the new points in the mail and had a few hours to work on it Sunday in between the rain.

I put the new points on, Set the gap on 1/2 at .016. hooked my test light on to the strap of 1/2 and the other side got grounded to the frame. loosened the screws holding the plate to allow me to rotate the plate to time it, and to my surprised the light came on. Okay I got lucky I thought, just need to tighten it down. As I did the light went off. okay loosen again, light stays off. I try to rotate to get the light on- absolutely nothing

I spent the better part of half an hour rotating the points plate every direction and could not get the light back on again. I checked the test light several times by connecting it to the battery and it worked just fine. I checked the ground spot I was using by hooking the light to the battery and the ground, again just fine. So the light was working. I checked to make sure the bike was in the run position and the key was in the on position, which they were.

Any ideas where to start looking when your points are seemingly not getting any spark? I am still am very new to motorcycles so is there a newbie mistake I am making here?
 
hmmmm ...it time to evaluate the ignition system ...needs pics of coils and all ...could be wrong parts set up or something like switch gone bad..... coils bad ....100 ignitions can be something else to get going after all the yrs on them...
 
Wiring to points must be on the right side of the insulator. It's very easy to wire them to ground. Check for a wire or connector touching ground. A good close up pic might reveal where the problem is.
 
Just wanted to say thank you for all the help you guys have been giving. I know you deal with newbies like me a lot and it is appreciated you being so patient.

It was a ground as Slabghost said. I had the pronged wire connector facing the wrong direction. When you hook the wire up to the point the connector sits out a bit. Without thinking about it I had it facing towards the base plate when the point was installed, which allowed it to make contact with the base plate. A simple rotation of the connector fixed that up.

But I have another question to see if I am doing it right, because I am really not sure if I did- I moved the cam lobe to the point where it was at its highest over the left point arm (1/2). Then I set the timing gap on 1/2 point at .016. So far so good. But then I went to set the timing for 1/2 and that is where I get fuzzy. Using the timing window I advanced to F1 and I hooked up my test light and Bam- the light was on. I was thinking I was lucky and got it right away. I loosened the plate and rotated it and there was a huge area where the light stayed on. Probably like 30-40 degrees worth of rotation. I am genuinely confused as all the tutorials I have read seemed to indicate there was one sweet spot where the light would come on, not a range of 40 degrees.

So to the question- Where am I supposed to set it in that range? Is anywhere in that range good as long as the light is on when it hits F1? Am I still doing something wrong that I am getting that wide of a range where the test light is on?
 
no your not...when the light comes on at f1 mark is sweet spot in setting it up... same on other side ...sometimes after the points are set move entire plate a little might find a sweet spot while running ...your doing fine it seems
 
The light should just come on (as you're rotating the motor) at the F1 mark. It should then stay on for about 30-40 degrees as you've observed. You want it dead nuts at f1. If it stays on until after you've rotated past the f2 mark, this is better than before the f2 mark, as this gives full saturation of the other coil. If it closes before the f2 mark, both coils are energized which due to the older nature of these ignition systems, might reduce spark capabilities. Same for the other set of points, on at f2 and stays on until after f1.
 
Okay I think I am getting to the bottom of this one :) You guys have been so helpful, I would not have been able to figure this out without your help

Okay got my compression tester in (yeah I know I should have done this a long time ago) but I didn't have a tester and didn't know anyone who did.

Readings were 1: 125 2: 130 3: 128 4: 125 considering the bike has sat for about the last 2 years I think I should be alright with those
 
And the big find of the day. I triple checked the points and the gaps on the new points breakers. All perfect, gaps set at .016 for both, both fire right at their respective F. Tried to start her up on a charged battery, nothing again. But hey, at least now I am not getting any backfire into the carbs :Egyptian:

Since the points seem to be ruled out then I moved on the next most likely culprit- the coils

Pulled my spark plug boots and checked the secondary coil resistance directly from the spark plug wire
1/2 coil- 18540
3/4 coil- 15250

I assume by the 1/2 coil being 4000 over recommended (14.5) that its shot?
 
I am eliminating one thing at a time. Eventually I will find the culprit, and maybe even have a completely new ignition system in the process :smilie_happy:

So coil replacement is next on the list. Just trying to figure out my options, as I am running points. I have a couple of options, but am trying to figure what is the best plan.
 

Latest posts

Top