carb guys come in for starting problem

**phillysrt4** · 05-14-2008, 11:01 AM

Very interesting problem and with my carb experience being limited (FI FTW! :) ) I need some ideas where to look for this odd problem.

A friend of mine has a 69 GTO convertible that seems to start fine when its cold, but if its warmed up and he goes to start it (e.g. at a gas station after getting gas) it turns over but wont start. He has to let it sit there for a long time before it will start up again.

Any ideas on what causes this or where I should look first?

Thanks

EDIT - its a holley 750cfm double pumper

**Rodeheaver's** · 05-14-2008, 11:06 AM

does it turn over hard or just regular speed? has he tryed to check for spark or fuel when the problem occurs???

**phillysrt4** · 05-14-2008, 11:26 AM

Originally Posted by Rodeheaver's

does it turn over hard or just regular speed? has he tryed to check for spark or fuel when the problem occurs???

on the cold start it starts "normally" as I understand the problem.

No check for fuel and spark yet. The car hasn't been started in a long time so we're going to do a fluid change and a new battery this weekend to get it running again, then try to sort out the problem.

I just dont see how it could be getting spark when cold but no spark when its warm- wouldnt the motor just die then when it was warmed up? Thats why I'm leaning toward either fuel or timing.

I was just hoping for some ideas to on things to check/adjust and see if they solve it before going on a hardcore hunt, or if someone has seen this happen before and there is a "likely cause" I can examine first.

**Hawkeye** · 05-14-2008, 11:33 AM

Like Rode said...does it turn over hard, meaning real slow cranking when warm? If so, your timing may be advance too much.

**phillysrt4** · 05-14-2008, 11:36 AM

Originally Posted by Hawkeye

Like Rode said...does it turn over hard, meaning real slow cranking when warm? If so, your timing may be advance too much.

ah.... he didnt say warm, so I assume he meant when the car does start how does it start (i.e. the cold start characteristic).

I was thinking a timing issue. Anyway, I'll ask and see what he says about the starting.

**TJH64** · 05-14-2008, 11:48 AM

Vapor Lock. Back in the day, quite a few of my friends had goats and firebirds, and they all experienced this condition. Pontiacs were notorious for this. What happens is the steel fuel line absorbs engine heat while the engine is running. The fuel is flowing and it is not an issue until the engine is shut down. The heat soaked fuel line then turns the fuel into a vapor, causing the hard start condition. The fix is to protect the fuel line along the engine with a thermal barrier. Hope this helps

**phillysrt4** · 05-14-2008, 11:51 AM

Originally Posted by TJH64

Vapor Lock. Back in the day, quite a few of my friends had goats and firebirds, and they all experienced this condition. Pontiacs were notorious for this. What happens is the steel fuel line absorbs engine heat while the engine is running. The fuel is flowing and it is not an issue until the engine is shut down. The heat soaked fuel line then turns the fuel into a vapor, causing the hard start condition. The fix is to protect the fuel line along the engine with a thermal barrier. Hope this helps

Thats something I totally didnt consider, and wouldnt be a bad idea to perform anyway just to rule it out.

Thanks! I'll get a thermal barrier in regardless, and then explore timing issues depending on what he says about the warm start turnover.

SCS pwnz all! :)

**Rodeheaver's** · 05-14-2008, 03:13 PM

what type of igniton?? also vapor lock could be happening...

**phillysrt4** · 05-14-2008, 03:41 PM

Originally Posted by Rodeheaver's

what type of igniton?? also vapor lock could be happening...

I need to get more details, but AFAIK that is all stock. I dont remember seeing an MSD or some sort of aftermarket part in there, but then again I havent seen it in about 2 years.

**wick** · 05-14-2008, 03:48 PM

I was going to say vapor lock but it seems to be covered already.

**Martin0660** · 05-14-2008, 09:30 PM

Originally Posted by wick

I was going to say vapor lock but it seems to be covered already.

X3 - check the routing of the fuel line, especially down at the fuel pump if it comes close to a header / manifold, or where it comes up to the carb. Think heat soak in our world ;)

Bob Myers

**phillysrt4** · 05-15-2008, 10:52 AM

Originally Posted by Martin0660

X3 - check the routing of the fuel line, especially down at the fuel pump if it comes close to a header / manifold, or where it comes up to the carb. Think heat soak in our world ;)

Bob Myers

LOL got it!

gonna get a roll of manifold tape or something and wrap the line in the key areas to keep heat away from it and see if that helps.

unless someone has a better idea for it i'll use that. after that i'll start diagnosing other things but thats a cheap mod that probably should be done anyway.