340 hesitates

[1fastcuda]

Hi
Been having problems with hesitation on take off. Great at higher speed. This is a new restore 70 cuda 340 4 speed Has stock crank Eagle rods trw pistons x heads ld340 intake stock valve train. Running a purple cam 270 484 108 50 has 3.55 8 3/4 489 case Has Holley 750 carb. I have a stock electronic Dristubor stock coil stock plug wires Did not set cam to wheel. vaccumm about 7 at 900rpm everything new. What timing mark should be used.Number on the dramper > Just when i take off very doggie any idea's thanks k

 

[6packcuda]

When you say you have hesitation, do you mean it cuts out or stumbles or it just doesn't have any bottom end power? If it stumbles when you stab the throttle, it's probably carburetor related. If it just doesnt' have any bottom end power, could be ignition timing or cam timing issues. Was the cam installed straight up, advanced, or retarded?

 

[moparal]

7 vacuum with that cam is low. sounds like you need to degree the cam in, if your tune is right. Dog on the bottom with 355 gear and a 266 first geer leeds me to think that and 7 at 900

 

[robert zver]

Hi
Been having problems with hesitation on take off. Great at higher speed. This is a new restore 70 cuda 340 4 speed Has stock crank Eagle rods trw pistons x heads ld340 intake stock valve train. Running a purple cam 270 484 108 50 has 3.55 8 3/4 489 case Has Holley 750 carb. I have a stock electronic Dristubor stock coil stock plug wires Did not set cam to wheel. vaccumm about 7 at 900rpm everything new. What timing mark should be used.Number on the dramper > Just when i take off very doggie any idea's thanks k

first I would eliminate any vaccum leak around the carb. and intake and vaccum lines.Next check the carb.shooters to see they have a good shot ....ROB

 

[1fastcuda]

have timing set at 10 just when i take off alittle stumble then gets better once you get going.is there a better way to time the motor without a degree wheel now.?? What would be a good number to set timing at. can you tell me would it be better to buy a after market distributer and coil to help the problem with better spark. or leave it stock dist coil thanks

 

[Aussie Challenger]

Replacing the ignition first is not the answer, 10 deg on the dist won't cause low vac unless you set ignition timing with vac. advance connected. More advance usually is required, possibly 15* - 18* but as said above check for vac. leaks, 7" is a very low number.
Disconnect & plug all external vac lines from the carby/manifold, if the vac. doesn't come up and timing was set correctly then it possibly could be the cam timing. Take off a rocker cover and check valve timing against the cam manufacturers spec's using a degree wheel should be a quick way of testing if the cam is correct. If it looks wrong then the front will have to come off and be set up properly.
It always pays to check cam timing when installing so if a problem like this comes up it can be eliminated. A quick check of accelerator pump operation should also done.
If the vac does come up with all vac lines off then you need to put them on one at a time, power booster leaks can be harder to find sometimes.

 

[1fastcuda]

I have the timing on the money. My vauccum reading at 1000rpm is 7 bad checked for leaks found nothning. Deciding if i should go to a non vaccumm adv dist. Would this help??? The stock dist I have came out of a 1977 dodge truck. Thats what i had to use at the time. Not sure what to do thanks

 

[burntorange70]

A non vac dis would not help. Try more initial timing but if you do that you may need to limit the micanicel adv in the dist if total timing is over 35*. Your motor will like more of a performance advance curve. Also would be nice if total micanicle advance was coming in at around 2500-3000 RPM. Try setting total timing at 35* if you can.

 

[1fastcuda]

Ok I will been working on the timing Today got vac at 10 at 1000rpm. my initial timing is at 10 deg it starts right up when warn so must be close. there's no starter drag like if timing was off. checked vac leaks found none. At idle was i step on it there's quite a hesitation ( quite a bit).Above 1500 runs good only at idle taking off . Help if you can

 

[6packcuda]

Did you check to see if you're getting a good shot of fuel from the accelerator pump? With the engine off, just look down the carburetor and open the throttle by hand. You should see a pretty strong stream of fuel shoot into the throat of the carb. If not, your accelerator pump diaphragm could be shot. Easy fix.

 

[1fastcuda]

Plugged off brake booster and carb got about 9in vac at 1000rpm. Starts right up no problem. has a holley 750 not a double pumper. You guys say degree the cam if its starting right up would that still be the problem. My vac gauge bounce's around like 7-10 My freinds chevy has 15vac and very steady.I appreciate the help. When i step down on it hesitates then goes.
Is it possible carb is not big enough. Has a LD340 Intake x heads.

 

[1fastcuda]

I have plenty of gas in the carb shoots right out. This carb has 2 air mixture screws. I've read that alot of carb's have 4 would that be a problem. Looking at different options before i have to tear apart. Thanks

 

[1fastcuda]

Got it Fixed Had a freind come up and found out the Power Valve in the carb was bad. When we pulled the carb of noticed that the gasket had gas all around it. Base of carb was gas wet to' So we put a 1in spacer on the ld340 and Put it back together Got it running and had know hesitation and vac was 15. Want to thank all you will your help. Glad to know there's sites on the internet for help thanks again.

 

[6packcuda]

Glad you got it figured out. Now I want to see a burnout.

 

[burntorange70]

Good to here she is running better for you. I too put a spacer on my 340. Helped out a lot with heat soke.