Bog or delay under wot?

[Olive1970]

I have had this issue with my newer engine that I put in. If I put the gas to the floor it will bog or not have the same response as above say 3500rpms or so? After that it will come alive and just wrap the rpms up, where as before 3500rpm the delay is obvious on the tach.

The truck has HEI, Holley 650 spreadbore, built TH350 with 2200 stall converter.

The engine is: 350 bored 40 over, flat top pistons, 1.94/1.60 valves, double roller, weiand intake, z28 springs, bunch of new factory parts, and a pretty rough cam int exh
dur@.050 234 244
valve lift .488 .510
lobe sep 107 117

I am thinking this is a distributor advance issue? Maybe time to swap springs or make some other mods to the advance? Or time for a different dist?

Thanks all, spring is coming

[Longhorn 70]

Too much squirt?? Just a guess

[TBONE1964]

How does it idle just sitting in park? You have a good idea checking the mechanical advance springs and also it sounds like it may be wanting more fuel in the secondarys. If I remember correctly the spreadbore holleys are double pumpers. Is the secondary accelerator pump working?

Have you run this carb on a different engine and how did it work?

[Olive1970]

Originally Posted by TBONE1964

What are you running for a transmission? If it is an automatic, do you have a stall converter. With that cam, I would want at least a 2800 - 3000 stall.

How does it idle just sitting in park? You have a good idea checking the mechanical advance springs and also it sounds like it may be wanting more fuel in the secondarys. If I remember correctly the spreadbore holleys are double pumpers. Is the secondary acceletor pump working?

Have you run this carb on a different engine and how did it work?

The trans is a TH350 that is rebuilt with upgraded clutch pacs and a shift kit, etc. I have a 2200 stall converter. Just sitting in park it idles fairly well but have it bumped up to 1000rpms for the drop when putting into drive or reverse.

This is the first time running this carb on this engine. It is only a single feed for the secondaries. I ran a squarebore Holley 600 before but it was struggling to run with that, just about maxed out. The only thing I haven't messed with is the distributor.

I am running 18* initial timing and 36* at 3k rpms but of course I dont know how well the response is when setting the timing.

[TBONE1964]

That truck should light up like the forth of July with your combination of parts. I would try (like you suggested) stiffer mechanical advance springs. It may be pulling everything to full advance way before it needs to. If that does not work, I think I would consider a true dual feed double pumper carb with mechanical secondarys. I have never been a huge fan of transfer tube vacuum secondary holley carbs for the very reason of the problem you have.

[Olive1970]

Originally Posted by TBONE1964

That truck should light up like the forth of July with your combination of parts. I would try (like you suggested) stiffer mechanical advance springs. It may be pulling everything to full advance way before it needs to. If that does not work, I think I would consider a true dual feed double pumper carb with mechanical secondarys. I have never been a huge fan of transfer tube vacuum secondary holley carbs for the very reason of the problem you have.

I was hoping that the truck would, but know that something is missing here. As far as the advance springs, would I want to go stiffer so it comes in later? I would have thought to go with a lighter spring with my issue, could be way off though.

I have considered a 750 dual feed double pump. Holley has a new one with electric choke but at a hefty price tag. Maybe sell the two used ones I have and go from there also, try something with distributor first.

[TBONE1964]

That is a good question. My thought is that if you use a light spring/weights, then the advance comes on quicker. Is it coming on to quick and causing your problem? Hook you timing light up to it and disconnect the vacuum advance. Then slowly rev the engine up and watch the timing mark. How fast does the mark move when you accelerate? It should match your speed.

I found this link on the web that may help you understand the way the mechanical advance works and how to set it up.

http://www.pontiacstreetperformance....distcurve.html

Hopefully, you can sort it out. I will be curious to know what fixes your problem.

[Olive1970]

Originally Posted by TBONE1964

That is a good question. My thought is that if you use a light spring/weights, then the advance comes on quicker. Is it coming on to quick and causing your problem? Hook you timing light up to it and disconnect the vacuum advance. Then slowly rev the engine up and watch the timing mark. How fast does the mark move when you accelerate? It should match your speed.

I found this link on the web that may help you understand the way the mechanical advance works and how to set it up.

http://www.pontiacstreetperformance....distcurve.html

Hopefully, you can sort it out. I will be curious to know what fixes your problem.

It will be a little difficult to identify how well the mark responds, since the 18* initial timing is at the top of the time tab. But it should be something that can be done now that there are electric fans only.

I should be able to sort it out in time, bothers me too much not to! Thanks for the advice

[Lattimer]

Originally Posted by Olive1970

It will be a little difficult to identify how well the mark responds, since the 18* initial timing is at the top of the time tab. But it should be something that can be done now that there are electric fans only.

I should be able to sort it out in time, bothers me too much not to! Thanks for the advice

18 degrees sounds like an awful lot of initial advance. How did you wind up using that much?

Different engine I know, but my 327 from what I have read was supposed to have anywhere from 2-6 from the factory depending on which version. The higher output versions got 8. I have read to add as much as 4 degrees with the ethanol fuels.

[Olive1970]

Originally Posted by Lattimer

18 degrees sounds like an awful lot of initial advance. How did you wind up using that much?

Different engine I know, but my 327 from what I have read was supposed to have anywhere from 2-6 from the factory depending on which version. The higher output versions got 8. I have read to add as much as 4 degrees with the ethanol fuels.

A lot of my timing had to do with starting the truck up, it will fire right up with this much timing. The engine would do ok with 12 degrees on starting but the idle was not as smooth and the driveability had some issues when accelerating, even more so than the issue I have been having. There is no spark knock or pinging with the current timing setting.

[bowtie72]

How is your truck under load? Does it climb hills fine? I think I would look at the carb secondaries. Holly makes the quick change secondary spring kit. I would say your secondaries arent working correctly meaning opening to slow or to fast. Does it come out of the bog if you hold your throttle position? Or does the engine die?

[Lattimer]

Originally Posted by Olive1970

A lot of my timing had to do with starting the truck up, it will fire right up with this much timing. The engine would do ok with 12 degrees on starting but the idle was not as smooth and the driveability had some issues when accelerating, even more so than the issue I have been having. There is no spark knock or pinging with the current timing setting.

Are you sure your zero mark matches TDC?


Something just doesn't sound right to me. Not an expert by any stretch, but it seems like it should be pinging like crazy under load, and your total advance would be higher at RPM.

[Olive1970]

Originally Posted by bowtie72

How is your truck under load? Does it climb hills fine? I think I would look at the carb secondaries. Holly makes the quick change secondary spring kit. I would say your secondaries arent working correctly meaning opening to slow or to fast. Does it come out of the bog if you hold your throttle position? Or does the engine die?

Under load is when the bog seems to come on when the throttle is down, but seems to be before 3500rpms. The truck seems to do fine when climbing hills but of course I have to give it some throttle. If I keep holding the gas down under full throttle it will come out of the bog, but only after 3500rpms or so. This engine spins 6500 no problem.

[Olive1970]

Originally Posted by Lattimer

Are you sure your zero mark matches TDC?


Something just doesn't sound right to me. Not an expert by any stretch, but it seems like it should be pinging like crazy under load, and your total advance would be higher at RPM.

That much I am sure of, I verified of zero mark at TDC when I first installed the new engine in the truck. Total advance is higher, to be honest I am surprised at the amount of time a bit too. But never an issue with pinging at the current setting.

[Lattimer]

Originally Posted by Olive1970

Under load is when the bog seems to come on when the throttle is down, but seems to be before 3500rpms. The truck seems to do fine when climbing hills but of course I have to give it some throttle. If I keep holding the gas down under full throttle it will come out of the bog, but only after 3500rpms or so. This engine spins 6500 no problem.

That sounds like the secondaries aren't adjusted right.

Mine will bog like that for a split second when the secondaries first open if you punch it from a roll, but it comes right back to life. I have an Edelbrock 1406.

[Olive1970]

Originally Posted by Lattimer

That sounds like the secondaries aren't adjusted right.

Mine will bog like that for a split second when the secondaries first open if you punch it from a roll, but it comes right back to life. I have an Edelbrock 1406.

That is very possible, I might not have found the right carburetor for this engine yet. As suggested above I could always change to a different spring on the secondaries, or use a carb with mechanical I suppose. I know my particular Holley carb performs well on a stock 350, but maybe not so well on mine.

[Lattimer]

Originally Posted by Olive1970

That is very possible, I might not have found the right carburetor for this engine yet. As suggested above I could always change to a different spring on the secondaries, or use a carb with mechanical I suppose. I know my particular Holley carb performs well on a stock 350, but maybe not so well on mine.

Mine has mechanical secondaries. Works fine if you ease into it, but if you really punch it, it bogs for a second, then roars. I'm new to carbs, never owned anything bigger than a lawn tractor that didn't have fuel injection. So I'm not sure if my issue means too much or too little fuel. Not a big enough issue to dig into yet.

[68Cummins]

What model Weiand do you have? I had the X and it reacted the same way, sluggish on the bottom. Thumbing through Jegs catalog and Weiand recommened 3200 stall.

[Olive1970]

Originally Posted by 68Cummins

What model Weiand do you have? I had the X and it reacted the same way, sluggish on the bottom. Thumbing through Jegs catalog and Weiand recommened 3200 stall.

I have an older Weiand, but it is very similar to the Street Warrior 8125.