throttle response problems.....

[rubbinsracin]

we have no problem as long as the throttle is rolled into, however, if you just punch it, there is like a second and a half delay then the (not a nice word)(not a nice word)(not a nice word)(not a nice word) thing roars like a champ. what could be the problem?

we run a DLM with an 11-1 383 in our "crate/gn" class with a victor jr intake and a holley 750 (72 front and 74 rear for jets). we run a mechanical fuel pump that is rated for 9psi but when you really get on it the pressure on the gauge tends to be higher than that. is it possible we need a pressure regulator because we have to much pressure?

we have ran "track gas" which was 110octane and now this year we are going to run Aviation fuel which will be right in that range, that will be given to us by a sponsor. we have our timing set at about 33-34*. also after the engine warms up it still has a delay but not near as bad.

[Egoracing]

Aviaton fuel dry and not made to atomize at ground level (unless you race 10,000 feet above sea level). Do you and your engine a favor and do a search on here before running it. Av 110 octane and racing 110 octane are NOTHING alike.

[rubbinsracin]

yeah i have read that, but with the budget tight and cost for racing fuel at the track going to to $8/gal were going to run the AV fuel. the guy who is giving it to us at $2/gal gives it to 5 other racers that run our class at our local track and have since they opened the track 6 years ago. We will be the 6th. three of them run 604 and three of us will be running the steel head option. none have had any trouble with the fuel at all. in fact 4 of the 5 that previously ran it finished in the top 7 in points and the other was 11th. so its good fuel in my opinion.

i guess what im saying is any help with the problem we have would be greatly appreaciated and i will head your warning about the fuel.

[dirtrace09]

Check your float level in the rear bowl. Also check your accelerator pump to see when it is giving its shot.

[rubbinsracin]

Check your float level in the rear bowl. Also check your accelerator pump to see when it is giving its shot.

Thank you for the info! Where should the float level be approx and how would we check the accelerator pump? sorry carbs are not my forte

[sj valley dave]

Sounds to me like it is an accelerator pump issue...Make sure they both are operating correctly and the pumps arms are adjusted correctly...Size of squirters and pump cam might need to be tweaked also...

[Moldymulldoon]

Go UP a few sizes on the shooter. Check the cam could be wore? Check pump arm make sure its adjusted right. Wide open use a .015 feeler gauge between pump arm nut and end of pump arm. 'So it doesn't bottom out the diaphram.
Too big a shooter size the engine will feel lazy, possible to see black smoke out of exhaust. Too lean, dead spot and popping of carb.
Try an orange cam. On front half of carb. 4bbl right?

I have seen a carb with a 30cc arm on a 50cc pump... doesn't work very well set up that way.

Hope this helps some.

Moldy

[DaveBauerSS6]

I've fixed numerous bogs on 2 and 4 bbls, by sizing down on the accelerator cam. Too much fuel and it will not always show rich smoke. I normally get the job after the accel system and /or jetting was richened. Rich or lean acceleration in the car feels the same to me. Dropping the power valves 1 number can delay extra fuel also.

Been on the dyno with 100 LL AV fuel . It burns slower than race gas. Bumped up timing 36 to 40 degrees to get the same numbers. Never had a problem related to AV fuel.
Good luck.

[rubbinsracin]

I've fixed numerous bogs on 2 and 4 bbls, by sizing down on the accelerator cam. Too much fuel and it will not always show rich smoke. I normally get the job after the accel system and /or jetting was richened. Rich or lean acceleration in the car feels the same to me. Dropping the power valves 1 number can delay extra fuel also.

Been on the dyno with 100 LL AV fuel . It burns slower than race gas. Bumped up timing 36 to 40 degrees to get the same numbers. Never had a problem related to AV fuel.
Good luck.

so what would be the best way to set this carb up?

as stated before its a 383 11-1 with camelback heads 202-160 of course. victor jr intake, fairly hot flat tappet cam. its a holly 4150 with 72-74 jets in it. has the cam on it that came with the carb.

[DaveBauerSS6]

Color POS1 POS2
White 17 19.5
Blue 18 20
Red 18.5 20
Orange 19 24
Black 19 18
Green 24 30
Pink 30 37.5
Brown 36 N/A
The value next to the color is cc amount of fuel delivered on one stroke. Less number less fuel.

Check the color and position of the primary cam. you will see a 1 or 2 next to the screw hole. Drop the color or hole by 1 step. Do the same for the secondary. Run the motor at the track and compare the change; if its better go another step. If it gets worse you are likely lean, go the other way. As Moldy said set the cam arms correctly. No gap at closed throttle, safety gap at WOT.

Cracking the throttle in the garage is not the way to check the results; do it on the track.

Stock carbs were built for street performance, not for a 383 11.1 cammed monster on a dirt circle track between 4000 to 7400 RPM. They need some tweaking.

4412 2 bbl 500 - I drop from the brown to green 1 and its fixed. Depending on the combo, you may have to go down 2 steps on a 4bbl, has been my experience on a 4bbl.

You should check your power valves also. One half your idle vacuum minus 1 on both ends. IE 10 in vac at idle warm, half is 5 minus 1 = 4 power valves. If they are to close, they can open earlier and contribute to the rich condition.

I always run a regulator. 9 is too high. Regulate the pressure to 7PSI at all RPM. The extra pressure can vary the fuel level to much causing slight rich/ lean condition; minor but important.

Good luck.

[rubbinsracin]

so we finally had our first week of running the car. didnt do anything to the carb to see if we could replicate the issues from last year and correct it from there. Ambient temp was about 50* so when we pulled onto the track we were at a good operating temp. we had a full tank of fuel (about 2 gallons of VP110 and 20 gallons of AV) and we ran about 75 laps (it was play day) and never once after we got some heat into the motor did it lag at all. so when we got off we double checked the plugs just to make sure we were not fouling any plugs. they looked good and the motor ran cooler, smoother, and was more responsive than it had ever been! we told our motor builder we were running AV fuel and he said he ran it for 10 years before he went to an A-mod and runs methanol now.