Kinda dumb engine tuning question

[loco340cuda]

Moper and 72challenger, how much vacuum would you expect to see with my setup?

[422STROKER]

I agreed with MOPER cause he is building a 340 Stroker for me as well.  Same carb he mentioned.  Anyways i would imagine it would have very good vacuum with that cam and Motor size.  The additional Cubic inches you have make that SB Cam small.  It isn't too lumpy in a stock stroke 340-360 so in a 417 should be smooth.  Stock is over 15in vacuum?  Something like that, I'll let the smarter guys go a this.(Chryco+Moper and others here.)

Tom

[moper]

Iwas just thinking to myself here...the 9-10" of vaccum, was that hot in drive at 850-900, or was that just hot idle in neutral/park? I would expect a 417 with a cam that size to idle in park with at least 14" of vaccum. If there were minor issues like it being lean, or timing slightly off, or carb adjustments, perhaps it woud drop to 10-11 in park. But in gear, something running that poorly would pull like 8-9". If it was healthy in gear, I would be expecting the 10-11" reading at minimum. The cam is just plain mild in a 4" arm engine.

[BIGSHCLUNK]

Are you sure your mixture is right?? Throw a vacum gauge on the carb and play a little........ 

[Justins72]

Sorry if i hijack the thread but im having the same problem with my 340 that only has a .30 over bore. Where do you hook up the vacum gauge too?

[loco340cuda]

Ok, here's an update.  I went out and let the car warm up this morning, I had a hard time getting the car to stay running.  I have a problem with the choke and fast idle that I can't seem to get right, but since I'm here in Arizona the car warms up pretty quickly so no big deal. 

Once the car was warmed up I checked the timing and it was at 18.5deg at idle (close to what I was told to set it at with my FBO curved distributor, they said 18deg). I checked the idle and it was about 900rpm (The car was in neutral ,car is a 4-speed).  I checked the vacuum and it was at 12".  I messed around with the A/F mixture screws but I could not get the vacuum to go any higher then 12" but I could get it to go lower and almost make the car stall.  So set the vacuum back to 12" and rechecked everything. 

Next I did a vacuum leak test with propane.  I checked all around the base where the carb meets the intake as well as on both side were the intake meets the heads.  As I did this I never saw a change in idle speed.  So I decided to take it out for a drive.  The car seemed responsive when I drove it and it did not seem to bog or have any dead spots.  When I stopped at a stop light the the car shook a little but not much, and nowheres near like how it shook last weekend.

After I came back from the drive I checked things again and they looked the same.  I also noticed the engine seem to idle more smoothly, not rocking the car like it did last week (well maybe just a little).  So the car seems to be doing better this week but I'm not conviced I'm out of the woods just yet.  I will feel better when I can start the car when it is cold and it idles at a higher rpm do to the fast idle circuit.

Another thought I had this morning that might explain why I'm seeing differences from last week to this week (considering I haven't changed anything) is that I had about 3 gallons of gas in the gas tank that sat there for about 3 months while the motor was out.  When I drove the car last week I filled up the tank.  I'm wondering if some of my problems were due to the old gas.  Any thoughts on that one?

[loco340cuda]

When I started the car up this afternoon (after it sitting for a few hours) it did the hard start again.     It is like it is missing in certain cylinders and as long as you keep the engine reving at higher rpm it slowly clears up with in about a minute.  I'm starting to think the carb is somehow flooding.  I checked the front float last week and it seemed to be at the correct level.  Is there something else I should check with these Holley carbs that might cause flooding?

-Thanks

[Bullitt-]

You mentioned earlier that there might be choke clearance issues, has that been thoroughly checked?    My experience, non-electric chokes, has been that a warm motor may still need some choke but is not getting it due to latent heat keeping the choke open.    This also reminds me of another member here that was having intermittent problems & it turned out to be the rebuilt distributor was not keeping the rotor button in position.

[BIGSHCLUNK]

Sorry if i hijack the thread but im having the same problem with my 340 that only has a .30 over bore. Where do you hook up the vacum gauge too?

Look for a port on the lower part of the carb/take a hose off or cap off ad put the gauge there. Thats usually a good spot. I you have a port on the intake that'll work too.

[moper]

I'm still waiting for a compression test result... althought the tuning seems to help ,the engine should start right up...

[loco340cuda]

Thanks for following up moper, I did not get a chance to do it on Saturday.  Before I get to that, the next thing on my list to do is investigate the choke and fast idle issue, I think this is my culprit with the startup problems.  When I got the engine back from the engine builder I noticed the choke was installed up side down, I'm guessing he did that to disable the choke for break in on the dyno.  I never checked it when I first got the carb since I assumed the carb was new and there shouldn't be any issues like that. 

Anyway, the thing I have noticed with the hard startup issue is that the fast idle never kicks in (i.e. after the car is started it never runs at higher rpm due to the fast idle circuit).  I need to go review the procedure to set the choke as well as adjust the fast idle screw to see if I can get the car to idle at higher rpm on cold starts.  Once I see the carb acting like I think it should then I can have some confidence that I have a good baseline to start tuning from and see if I truly have some other issues. 

I'll keep you posted on what I find out.  I'm going out of town for a week and half so it maybe a little while before I have an update.

Cheers!