I have not been able to get this 350 build to idle out right. Timing is around 12 degrees, keep lowering float level but idle is fuel rich fat. my first question is Idle eeze adjustment, I'm currently about 2 turns out but no rpm change
street demon carb with thumpr cam
- Thread starter flew
- Start date
- Joined
- Dec 21, 2012
- Messages
- 181
- Karma
- 19
- Location
- Jeffersonville, Indiana
- Car
- 1929 Buick, 1957 Chevrolet
Hi flew,
Welcome to the forum. There can be several things going on here. Are you checking the timing with the advance disconnected? When you say it has a thumper cam, how well do you expect it to idle? What kind of vacuum is the engine pulling and at what RPM? What all have you done to the engine and what size is it?
With the sight plugs removed in the side of the float bowls you should adjust the fuel level so that is is barely under the hole, that should be sufficient. Have you checked for vacuum leaks, how are the valves adjusted and do you know for sure the engine is times right? There are several things I need to know before I can help.
I don't mean to insinuate you don't have it set up right but I can't see or hear the engine run and I am going to have to guess at all of this.
Welcome to the forum. There can be several things going on here. Are you checking the timing with the advance disconnected? When you say it has a thumper cam, how well do you expect it to idle? What kind of vacuum is the engine pulling and at what RPM? What all have you done to the engine and what size is it?
With the sight plugs removed in the side of the float bowls you should adjust the fuel level so that is is barely under the hole, that should be sufficient. Have you checked for vacuum leaks, how are the valves adjusted and do you know for sure the engine is times right? There are several things I need to know before I can help.
I don't mean to insinuate you don't have it set up right but I can't see or hear the engine run and I am going to have to guess at all of this.
- Joined
- Dec 21, 2012
- Messages
- 181
- Karma
- 19
- Location
- Jeffersonville, Indiana
- Car
- 1929 Buick, 1957 Chevrolet
Flew,
I would also need to know the specs of the cam if possible.
I would also need to know the specs of the cam if possible.
This is the smaller thumpr cam 241 duration. I keep lowering float level. Idle vac was 6 to 8 in gear. Power valve is now 3.5 and I have not touched the secondary vac spring yet. I have used the demon carbs on other builds and have had super results. I"m going to check the base plate gasket today. When I first started this engine the back float bowl would not get fuel found a bee in the needle valve how he got there ?
Nobody got a clue out there? Timing is now set at 18 degrees, float levels at bottom off window, distr advance set to 16 degrees , vac is 10 . Running alot better but its not there yet. I would not recomend this thumpr cam to much dialing in for to little bite but it does have a loud bark
- Joined
- Dec 21, 2012
- Messages
- 181
- Karma
- 19
- Location
- Jeffersonville, Indiana
- Car
- 1929 Buick, 1957 Chevrolet
Flew,
That is not much vacuum, even for a cam like that. How do you have your valves set, is it possible they are too tight? Is that 16 degrees of timing with the advance unplugged and the vacuum port on the cab closed off?
I am concerned about the 16 degrees of timing. How does it run with that much timing? Reason I ask is many years ago when I was a younger man I rebuilt an engine for a man and it ran like crap. I wound up having to set the timing on about 32 degrees at an idle. I thought "This can't be". Turns out the harmonic balancer had either slipped or was the wrong one for the engine. The timing marks were in the wrong place. I never considered a problem like that, but I changed the balancer and it indicated the proper timing.
I told you before that Chevy liked a lot of timing for performance use, but 16 degrees is a lot. I have felt comfortable with as much as 12 BTD, but more than that????? Have you checked for vacuum leaks around the carb base and the intake manifold? With a can of Gumout spray Carburetor, spray it around the edges of the intake and around the carb and base plate. If you get any kind of a change, you have a vacuum leak.
The way I see it there can be several things that can be wrong.
Valves too tight.
Harmonic balancer possibly slipped indicating the wrong advance.
Vacuum leak around the base of carb or around the intake.
Timing marks aligned on the timing chain incorrectly.
Did you put a high performance timing chain in it? Most of the after-market timing chains has 3 sets of timing marks. Is it possible that you chose the wrong ones? I did a dumb trick like that once a long time ago myself, being unfamiliar with the 3 sets of marks. I learned some things the hard way.
That is not much vacuum, even for a cam like that. How do you have your valves set, is it possible they are too tight? Is that 16 degrees of timing with the advance unplugged and the vacuum port on the cab closed off?
I am concerned about the 16 degrees of timing. How does it run with that much timing? Reason I ask is many years ago when I was a younger man I rebuilt an engine for a man and it ran like crap. I wound up having to set the timing on about 32 degrees at an idle. I thought "This can't be". Turns out the harmonic balancer had either slipped or was the wrong one for the engine. The timing marks were in the wrong place. I never considered a problem like that, but I changed the balancer and it indicated the proper timing.
I told you before that Chevy liked a lot of timing for performance use, but 16 degrees is a lot. I have felt comfortable with as much as 12 BTD, but more than that????? Have you checked for vacuum leaks around the carb base and the intake manifold? With a can of Gumout spray Carburetor, spray it around the edges of the intake and around the carb and base plate. If you get any kind of a change, you have a vacuum leak.
The way I see it there can be several things that can be wrong.
Valves too tight.
Harmonic balancer possibly slipped indicating the wrong advance.
Vacuum leak around the base of carb or around the intake.
Timing marks aligned on the timing chain incorrectly.
Did you put a high performance timing chain in it? Most of the after-market timing chains has 3 sets of timing marks. Is it possible that you chose the wrong ones? I did a dumb trick like that once a long time ago myself, being unfamiliar with the 3 sets of marks. I learned some things the hard way.
Is there anyone out there that is running this cam? I'm still running rich at idle and it is alot better moving timing, yes the cam was degreed, yes the valves are right, yes the balancer timing is dead on. find sight should have installed the extreme energy but the thumpr has had my interest.
