350 diagnostic help-- stumble stall when warm (1 Viewer)

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First start by making sure your fuel pressure is correct, your timing is correct, and then check for all the dumb stuff like plugs, wires, rotor button, etc... When does it exactly happen? Under full throttle, part throttle, under a load. Need more info. Seems like you have a lean fuel stumble if it runs good after that.
 

BMThiker

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Ok ladies and gents....

https://forum.ih8mud.com/40-55-seri...0tbi-stumble-stall-when-warm.html#post6464093

Please respond on the main forum so I can keep all the ideas together in one place.

Thanks
First start by making sure your fuel pressure is correct, your timing is correct, and then check for all the dumb stuff like plugs, wires, rotor button, etc... When does it exactly happen? Under full throttle, part throttle, under a load. Need more info. Seems like you have a lean fuel stumble if it runs good after that.
All suggested on the main forum already. Click the link he provided.
 

jfz80

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Cool, thanks guys. was being a bit link lazy and in a rush yesterday as well as trying to keep all the info together.

I can start the 45 and it runs fine....untill it warms up. Then it slowly lowers RPM and stalls.

I did get it started and keep it started by working the accel and drove it to a members house where it struggled horribly getting going in 2nd and 3rd but once up to speed it did much better but would skip/stumble if I tried anything past medium throttle input. top speed of 60, try for any more and it would start missing/stumbling.

When I advanced timing it ran well, even when warm but was undriveable. It would buck and surge as soon as the clutch was released and motor under load.
 
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My carb was doing the same thing the other day which is why I removed it for TPI. It looked like the paper filter was falling apart, so I figured it was fuel pressure problem. As stated in your link, I have a nice 12 psi Mallory racing pump that may deliver you the proper fuel pressure if you want to try it.

Jeremy
 
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This will probably help. I have heard that max psi on this pump is 14, but the max operating psi is 12. This graph explains it, running it beyond 12 psi and the gph drops quickly. At 10-12 psi you would be pushing 100-110 gph. Not sure, but I would think that is adequate fuel flow for a TBI 350 since a 4.3 TBI only needs about 35-50 gph I believe.

Jeremy
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jfz80

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Its back at the house after replacing the insufficient fuel pump. Thanks to all for the thoughts and offers of help.

I need to regroup and get some work knocked out but Ill be back for some tuning questions.
 

BMThiker

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Interested in how you work things out (Bertha has a 350 tbi too). We are running a Holley fp, but not sure what model. It's loud and whiney.
 

jfz80

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My original unidentifiable pump was loud but in a drdrdrddrdrd way. not whiney.

The new pump is a bit whiney but not as loud as some I've heard (a holley in particular)
My recomendations would be:
Carter P5001 / NAPA P5001 / Holley HLY-12-927 This is a self priming pump. It regulates out 9-22psi.
Master/Airtex E8094 is a medium pressure fuel pump made for the GM throttle bodies which run at 15 psi. It pushes 17-20psi at 50gph.

I would have chosen the carterP5001 if I could have found it overnight. Napa seems to have discontinued their version. I ended up with the airtex E8094 which a few others on mud have run. I still have a few issues I need to identify but I will keep you posted if it is fuel PSI related.
 

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