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Woodie

Woodie

Take-off EH!
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A little info..

..340 stroker (426) 10:00.1cr 32 degrees total advance @ 2800rpm. 904 Auto with 3500 stall.

-850cfm Pro-Form with #76 mains & #84 out back (#45 PV)
-Victor 340 intake with a 1 inch spacer.

When the mill is up to temprature 185 degrees, and Not under load, its has a stumble or hesitation ever so slightly. Also when at cruise, say around 3200rpm it seems to have a slight poping that can be heard through the mufflers. I belive it to be slighty to lean, the spark plugs are a very light rusty colour as well as the top of the pistons. Any thought on this would be great, looking for starting point to correct this problem.
 
First place I'd look would be the acellerator pump shot. Make sure it's good and strong.
 
StrokerScamp said:
First place I'd look would be the acellerator pump shot. Make sure it's good and strong.
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StrokerScamp... If its not that strong. does the pump need to be upgraded or can the disscharge nozzle just be changed to a larger size. I was wondering about the plastic cam that the pump-arm actuates on... Can that be swapped out..

P.S my shift key is fubar, question marks no workie.. see ÉÉÉÉ wtf.
 
Before I changed anything, I would make sure what's there is ok. Check for obstructions and such and make sure the pump arm spring and bolt are adjusted correctly. It may be that it's simply out of adjustment. If you start chunkin parts at it before you make sure it's in good tune, you might make it worse.....real quick.
 
StrokerScamp said:
Before I changed anything, I would make sure what's there is ok. Check for obstructions and such and make sure the pump arm spring and bolt are adjusted correctly. It may be that it's simply out of adjustment. If you start chunkin parts at it before you make sure it's in good tune, you might make it worse.....real quick.
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I agree 100%. Any links or websites for a flow chart set up? or is just know how and abilty the text book on this one.....:banghead:
 
Woodie said:
I agree 100%. Any links or websites for a flow chart set up? or is just know how and abilty the text book on this one.....:banghead:
Click to expand...

Didn't watch the whole thing but this may help?

[ame="http://www.youtube.com/watch?v=k-Nx5HEzvlY"]Mr. CarbTune's Garage - Accelerator Pump Tuning - YouTube[/ame]
 
Perfect. There's lots of little videos like that. That's what I was gonna recommend. There should be a bunch of those that will cover it all. They should help.
 
Idle speed screw open too far causing transfer slot issue, float level, then check pump shot.
 
Usually a bog of idle is associated with pump shot,like Stroker mentioned.

I would also bump my total timing up A few more degrees to around 36.
 
*Up date, Took advantage of some free time this weekend to do some tinkering After some research and trial and error I managed to tune the stumble out of the transition. Thanks to all that offerd a starting point. Turns out after rebuilding the carburetor to factory specs and reinstalling it I needed to make some changes. First the power valve was to big, the vaccum reading at idle in gear was only 9.5hg I replaced the #65 PV with a #45. I also replaced the the #76 Jets with #80 and left the #33 Shooters in. This combo was tested and found to be a little to rich and still had some stumble. I should also metion that I made sure the float level was as close to perfect as I could get it. I then instaled a set of clear site plugs, After swaping the main jets back to #76 and replacing the shooters from #33 up to #37 The difference was night and day! almost no stumble! I rechecked the timing at this point; total advance was 34 degrees @ 3000rpm. after a road test I knew there was still a little more to tweak. I poped in a fresh set of spark plugs. ( yes I bought 4 sets of eight! lol ) I moved the accelortator pump cam to the #2 position and took it out for a road test. Perfection! no stumble, no hesitation, and pulls Hard! Now I will put some miles on it and see what happens. Thanks guys for your input and with all the "Frigg'n with the Rigg'n" my level of comfort has improved with a little book reading and tuning. Now the car is really fun to drive!!
 
Demon 408 said:
Tell us more about your distributor and timing. Vacuum advance? Initial timing? Total timing?
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My 2 cents on this. Sounds like it has very little initial timing in it. Especially if it's a MP distributor or a MSD OOTB with no adjustments. If the car cranks for a while before firing, that's usually not enough initial in most cases. Bump the key and it fires right off, you have it close.

This might sound harsh... Setting timing on a street car using the total timing method is a rotten way to do it. Race car only, fine, even then not my favorite and only in a pinch.

Something to try. If you twist in a few more degrees of timing at idle and the engine picks up rpm, it doesn't have enough initial timing on it. If the engine has any kind of performance cam, setting the initial in the 15-22 range will be about right. Try setting it in that range and see how it idles and starts if it's not there now. Don't drive or hammer on it unless the total number gets fixed.

A 37 squirter is huge on most of these set ups. Primaries should not require more than about a 31 in most cases, 35 on secondaries.

My suggestion would be to get the initial timing adjusted so that's correct first, adjust mechanical to hit your total number, then tune the carb up.
 
crackedback said:
My 2 cents on this. Sounds like it has very little initial timing in it. Especially if it's a MP distributor or a MSD OOTB with no adjustments. If the car cranks for a while before firing, that's usually not enough initial in most cases. Bump the key and it fires right off, you have it close.

This might sound harsh... Setting timing on a street car using the total timing method is a rotten way to do it. Race car only, fine, even then not my favorite and only in a pinch.

Something to try. If you twist in a few more degrees of timing at idle and the engine picks up rpm, it doesn't have enough initial timing on it. If the engine has any kind of performance cam, setting the initial in the 15-22 range will be about right. Try setting it in that range and see how it idles and starts if it's not there now. Don't drive or hammer on it unless the total number gets fixed.

A 37 squirter is huge on most of these set ups. Primaries should not require more than about a 31 in most cases, 35 on secondaries.

My suggestion would be to get the initial timing adjusted so that's correct first, adjust mechanical to hit your total number, then tune the carb up.
Click to expand...

THIS IS GREAT INFO. Thank you. As it is right now, with the timing set at 34 total (initial is around 15-18). if you so much as breath on the key it fires right up. I have "Piggy-Back" timing computer for a 6AL i wanted to try. What are your thoughts? If the #37 squirter is huge, I would assume I am correcting around an issue that needs to be adressed? If so any thoughts? I can go back to my starting point and start over if this is the case.
 
Try advancing it at idle to 17-18 and see if it picks up rpm without touching anything else. You could also advance it until it kicks back or drags hard on the starter when warm. If it's more than about 22* set it at 20-22 and then limit/curve the distributor for the rest of your advance. See how it idles there and readjust the carb. Might run even better. It's good that it fires right off when you hit the key, that's usually indicative that you are in the right range.

If you can't tell, I'm in the "put as much initial as it will handle" camp when setting timing. Setting using total is too dependent on how much advance is in the distributor. Same engine with two distributors, one with 28*, another with 16* mechanical. Total time that engine with each at 34*. You'll have two entirely different idle/carb setting profiles. One will be MUCH better than the other. Some distributors are notorious for advancing far beyond 3K rpm, so that's another ill. The engine needs to be revved up until it stops advancing, if that's at 4500, then that's your real total number.

Initial is pretty cam dependent. Bigger cams usually like more initial. Being it's a 420+ inch engine and not knowing heads/quench, etc., hard to garner a total number. Most stroker quench style engines I've been around rarely liked more than about 32* total, some as low as 28*. Open chamber heads sometimes get away with more.

If you have a blue accel pump cam around that might be a good choice.

Good luck with it.
 
I'll just make a comment on the acc. pump. That is a fairly large squirter, but if the pump cam in use isn't that large it may be fairly balanced as is. You do have a pretty large runner intake and the 1" spacer add's to the plenum volume so if it likes it let it eat. Some combo's are just different so i don't argue with what it likes:D. I have found that if your too big on the acc. pump system you will usually get a rich puff out the exhaust on the initial hit?
 
x2 on what Cracked said. I would be starting around 18° (with the largest bushing included in the MSD dist. box that should end up around 32° total. Also - the power valve - there are all kinds of ideas about proper sizing. I've even had Holley tell me two different ideas on it on the same day...lol. I think you are creating a lean condition that is far more prevalent than a little stumble by delaying the power valve enrichment. Remember it's the power valve that has to enrich in most driving conditions when the throttle is not pressed down hard or far. So I like to use the highest number that will saty closed at idle. I think if you replace the 4.5 with a 7.5 you'll be able to go back to normal on the squirtor. I've never had to use more than a 33, and normally it's the 31 even on big blocks. Also - squirtors are a double edged sword. There is only so much volume in each pump stroke/cam combination. The larger the squirtor, the shorter period of time the enrichment lasts. In a race car the engine will be revving higher faster and the airflow will be quickly picking up to run the carb off the mains. In a street car, that may not be the case and again, it goes lean at part throttle and light throttle cruise.
 
moper said:
x2 on what Cracked said. I would be starting around 18° (with the largest bushing included in the MSD dist. box that should end up around 32° total. Also - the power valve - there are all kinds of ideas about proper sizing. I've even had Holley tell me two different ideas on it on the same day...lol. I think you are creating a lean condition that is far more prevalent than a little stumble by delaying the power valve enrichment. Remember it's the power valve that has to enrich in most driving conditions when the throttle is not pressed down hard or far. So I like to use the highest number that will saty closed at idle. I think if you replace the 4.5 with a 7.5 you'll be able to go back to normal on the squirtor. I've never had to use more than a 33, and normally it's the 31 even on big blocks. Also - squirtors are a double edged sword. There is only so much volume in each pump stroke/cam combination. The larger the squirtor, the shorter period of time the enrichment lasts. In a race car the engine will be revving higher faster and the airflow will be quickly picking up to run the carb off the mains. In a street car, that may not be the case and again, it goes lean at part throttle and light throttle cruise.
Click to expand...

I will try this combo, and report.
 
*Update, I took Moper's comments and made some changes. The end results were as anticipated. The lean conditon is gone, there is no longer any stumble or hesitation. I removed the #45 pv as well as the #37 squirtor. I installed a #7.5 pv and reinstalled the #33 squirter. I fired up the mill and closed the idle screw to verify that the power valve would stay closed. It did, and the results were impresive. The plugs look much better and it feels good in the seat of the pants. Thanks Moper, once again great input. I am going to take the time to adjust the timing as previously described. Thanks Craked. And also all the other members as well.

Woodie.
 
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