hesitates

[sds10racer]

have a small hesitation when i launch below 2800. have a 750dp. has 50cc pumps, 31 squirters. the linkage isn't 1-1. should i go to bigger squirters and 1-1 on the linkage or something else. thanks, charlie

[SST4530]

How is the accelerator pump set up? Are you ft braking?

[sds10racer]

pumps are set up as per holleys' recomendations so as not to bottom out at full throttle. am footbraking. have a 3500 stall.

[jmarksdragster]

You should not need 50cc pumps on a 750DP, put the 30cc back on. Do you have mechanical advance in the distributor? Try running more initial and see if it goes away but don't run it out, you will have to much total possibly. If it does, limit the amount of advance in the curve to give more initial without changing the total, or bring it in earlier. All your info on the engine/vehicle would help.

[sds10racer]

carb came with 50s on it. should i have 50 in front and 30 rear or try 30 all the way. have tried dif timing. seems to like 34 total at 3200 the best for et. have mech advance and no vacume advance. don't have any black smoke when i launch is why i was thinking on too small of squirters.

[SST4530]

pumps are set up as per holleys' recomendations so as not to bottom out at full throttle. am footbraking. have a 3500 stall.

Not saying the other advice is wrong, just don't do more than one change at a time so you know what works.

First off, since your ft. braking set the front pump so when your staged and at stall speed, you haven't used the entire shot before you need it. The stumble could be caused by not having enough initial shot left. When your at launch RPM you should still have almost all of your front pump shot left. May have to mess with the nozzle size and pump cams to get it right. This should also help your launch. Definately keep the 50cc on the front, 30 on the back should be fine.

How much total timing are you running now and what RPM does your full advance come in?

[cepx111]

Good advise blittle common problem overlooked by most tuners when footbraking.


But I still have some questions on your set-up s10.

What size motor is this?
What tranny?
Rear gears?
Cam?
Intake?

I kinda need more info.

[Tod74]

I had a 700 dp I bought new (years ago) and it had the 50 cc pump on the back when new...it was on a mild 406 and it would fall on it's face when you stomped it...put a 30 cc pump on and problem solved

[sds10racer]

this is a 355 with a gm hot cam kit, vortec heads w 1.6 crane gold rollers, rpm air gap with 13/4 spacer. 4.86 gears, 31.10.50 w m/t. all this has got me down to 1.58-1.60 60ft and 11.74 1/4 mile and 115 mph. the timing at the time of these runs was 38 at 3600. have put a recurve kit in the dist and am going to mess with it at the track this weekend to see what will work best. am bringing up the rpm's to 2800 and leaving from there. any lower than 2500 and the hesitation comes in. it's a small one but enough to loose on the 60 ft time. the launch is hard enough to spin the rim 1/4 inc each time i leave. hope thats enough as i have to go back to work now :) thanks, charlie

[SST4530]

this is a 355 with a gm hot cam kit, vortec heads w 1.6 crane gold rollers, rpm air gap with 13/4 spacer. 4.86 gears, 31.10.50 w m/t. all this has got me down to 1.58-1.60 60ft and 11.74 1/4 mile and 115 mph. the timing at the time of these runs was 38 at 3600. have put a recurve kit in the dist and am going to mess with it at the track this weekend to see what will work best. am bringing up the rpm's to 2800 and leaving from there. any lower than 2500 and the hesitation comes in. it's a small one but enough to loose on the 60 ft time. the launch is hard enough to spin the rim 1/4 inc each time i leave. hope thats enough as i have to go back to work now :) thanks, charlie

Somewhere between 36 and 38 deg. should about right for that engine. If your spinning the rims in the slick you better get some screws in them. try some of the tuning techniques advised and I think your problem will go away. But remember do one change at a time. To many changes at once could make it worse and then you won't know where your tune up is. :)

[sds10racer]

already got the screws in after i found out the slipping. gonna check the obvious first and then start the changes. i've always only made one change at a time even on the customers equipment so i know what fixes them for refer. later on. thanks for the tips, charlie

[mytmouz]

Most net advice on the Vortec timing is around 31 to 32 degrees. Mine was happy at 34. Each combo is different though...

[sds10racer]

went to the track today. yesterday i put a curve kit in the dist finally. i know i know, should have done this a long time ago :) . set it at all in at 34' at 2800. switched the primary pump cam to a different spot. too it today and first run was pretty good. .006 reaction, 1.60 60ft and 11.71 et. went back and bumped the timing up to 38 all in and dropped down to 11.69. left it there and went best of 11.68. made it to final round and i think i got the tires too hot. spun real bad of the line and on the shift to second. still went 11.85 hitting the brakes at the end when i caught the other guy. he hit the stripe at the same time i hit the brake so i don,t think i would have won as i was just a little behind. was hoping he would break out. this was king of the track day. he went on and finished runner up. all in all i think i made headway with my problem. next race will tell me more as i didn't want to change anything as it was working good. consistant low 11.7's. thanks for the tips and suggestions,charlie

[SST4530]

Glad it's working out for you! :) Keep us posted on the progress and if you need any more advice just ask.

Bill

[sds10racer]

just thought i'd put an update on this old problem that i think is fixed as of the last race of the year. have to wait till next year to make sure. after trying a lot of different things in '09, about the only thing i got done was dropping my et down to 11.61 but still had the original problem, just at a little lower rpm. this year i started messing with the timing curves. slowed down in the et, still won a few races and was going rounds, but no change in the hesitation. finally at the last race i went to, had the timing back to where it was supposed to be and the et back down. went out for the first qualifying pass, hit the gas and hesitated so bad i had a 2.63 60'. let off, hit it and shot like a rocket. ran a 12.49/113mph. not happy, went to the pits determined to fix it before next round. remembering what blittle in an earlier reply suggested i went to the track carb guy and talked to him about the issue. he said he had another guy that had same problem and went and showed me what it most likely was. he said as i was bringing the rpm's up, i was taking the the pump shot on the primary side and making it smaller. he said to give the lever on front and back a lot of freeplay at idle. did that and went the next round ready to make a good pass as it felt good in the pits reving it up. ran real hard off the line and posted an 11.57/115mph. new best. then went out and ran the first round and won on double break out with an 11.502/115.49. ended up going out 2 rounds later, but was running consistant 11.55/115. so the problem is fixed i believe. sorry for the long post, but thought the whole story would be nice for you guys. so now it's bench racing for the winter. charlie

[chevyart]

charlie that all sounds logical, what the carb guy told you to do. im curious if you still get the complete shot(all the CCs) squirted in as you would seem to loose some of the depth of the lever compressing the plunger down. what do you think?. also one of the guys mentioned chasnging the plastic cams. they do the same thing as yiou did without putting slack in the lever linkage art

[sds10racer]

art, couldn't really tell if it got a complete shot as i was in race mode at the time. don't like to mess with too much when racing. i didn't give it as much freeplay as he said, just enough to make the lever free. it must be getting enough as it dropped all the incrementals down except the 60'. i suspect that was due to the tires were, for lack of any other way to describe it, chattering on the launch. i could check next year when i get it out of storage, it's a little cold and snowy out now.