throttle hesitation

[Iceman247]

I reset the timing with the advance unhooked and tuned on the carb a little, nice and crisp now thanks for the help on it guys

 

[Chryco Psycho]

Glad you got it solved

 

[burntorange70]

Right on!

 

[DetMatt1]

Excellent, glad to hear.

 

[AUSTA]

what did you adjust on the carb i still have one id like to put on the other 340 i am building

 

[Iceman247]

i think it was more of the timing than anything but after i set it to 38* with out the advance i had a little to much gap between the pump arm and the adjustment bolt and spring and then i used a vacuum gauge and tuned the air mixture screws to smooth it out and i have about 13 cm of intake vacuum

 

[moparleo]

Your vacuum readings are very low. Any modifications on this engine that you know of ?

 

[AUSTA]

Avenger 570

Thanks
good you got it sorted
I know my timing is good i will put a bit more tension on the pump arm see if it fixes my flat spot.

 

[Racer57]

If you have an AVS carb, tighten the air dam adjustment 1/4 turn.

 

[Iceman247]

i was thinking my vacuum readings were low also so i did a compression test and I'm between 110 and 125. this is a new rebuilt 1978 360 motor bored .020 flat top pistons heads have been shaved (don't remember how much) and reworked new valves and all with a 280/280, Lift .474/.474 cam.

 

[Chryco Psycho]

So you have 13 CM of vacuum or 4-5" of vacuum ? At idle in gear I assume ?
you need to install a 2.5" powervalve inside the carb for a reading that low , if the idle speed is surging that will be the power valve opening & closing .
The compression seems to be on the low side but this can be affected by a lot of things such as engine being warm , throttle open , cranking speed , duration & overlap of the cam not that yours is excessive & the piston height relative to the deck height . Even the gauge can be inaccurate but as long as the readings are within 10-15 % you are ok .

 

[Iceman247]

sorry i was wrong i have about 12 -13 in Hg of vacuum, but at idle in park. What do you think about these numbers: 1st # is cylinder, 2nd is compression, 3rd is leak down. i guess my thinking is the motor has less than 200 miles on it and thought the compression would be more around the 150-160 range.

 

[Chryco Psycho]

12" is better , probably drops off to 8" or so in drive & is about what I would expect from that cam
typically a 340 should be closer to 150 with true replacement pistons being slightly above deck , but as I said the reading could be low for any of the reasons I listed before , , the compression should also rise with more miles on it as the rings wil not have copletely sealed in yet even with a Plasma Moly ring set .
I would run it some more work it hard & retest when you have 1500 miles or more on it .

 

[AUSTA]

Im running a 340, KB243 with 18 thou off the top ( flush with deck ),E/Q heads 64.5 CC .039"gasket getting 138 PSI after 2000 miles definitely improved after 1,000 mile 280/280 Cam 110Degree

 

[moparleo]

When you do your compression test, do it this way. 1) lock throttle open. 2) use a remote starter button attached to the battery and starter terminals on the starter relay attached to the drivers fender well next to the battery. 3) crank the engine for 3 complete revolutions. You can do this wet and dry. This means either doing the test with a squirt of oil into the spark plug hole before you attach your compression gauge, like Marvels Mystery oil or whatever you have handy. Or crank the engine as is with nothing added to alter the readings. Crank the engine the same amount of revolutions to get a more accurate reading.

 

[Iceman247]

thanks for all the input everyone!!!

 

[Iceman247]

can someone tell me what this canister above my gas tank is for and where does the line go circled in red?

 

[Chryco Psycho]

OK this is part of the emissions added after 70 , the fuel became a sealed / non vented system so the four lines connect to a vaopr seperator , the red line probably went forward to the carbon canister under hood to reburn the fuel vapors .

 

[Iceman247]

will it hurt anything to just have that line capped off?

 

[Chryco Psycho]

Yes & no , with no way for air to get into the tank you could create a vacuum in the tank , but you can use a vented cap if you can fine one to fit