Engine shakes BADLY!!

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Rob-Crackedback had some 10* advance bushings for a MSD. Check with him as he may still have some.

Did you replace all the gaskets in the carb when you had it apart also making sure you removed all the old gasket material? Did you also eyeball the gaskets to make sure you installed the correct ones as sometimes there's just a little difference in some. Sounds like it's sucking air somewhere like a gasket isn't sealing. The 28 squirter is a little small IMO and the pink cams aren't very aggressive. They shoot fuel all the way through the range but most of the time a cam that gives a quicker shot (as long as it's not so much to drown the engine) will work better. If it were me I'd start with a set of orange cams and a 32 squirter up front.

Even when the fuel mixture is right on plugs over time tend to get carbon fouled, especially when you have a nasty cam like yours that requires a richer mixture than normal. The only time you can really get a correct read on plugs is when you first install them and take it for a wide open run shutting it down right at the end of the run (don't allow it to idle) then pull over and pull them out and look at them. As for the correct heat range that's determined mostly by the compression ratio and indicated by the heated spot on the plug ground electrode. You really need to stick a new set of plugs in it and run it a little then pull them and read them. Here's a link to a page on reading plugs

http://www.dragstuff.com/techarticles/how-to-read-plugs.html
 
I have some 10 and 14* MSD bushings.

Coughing back up through the carb when yu snap it open is likely a pump shot, sizing, cam or adjustment.
 
fishy68 said:
Rob-Crackedback had some 10* advance bushings for a MSD. Check with him as he may still have some.

Did you replace all the gaskets in the carb when you had it apart also making sure you removed all the old gasket material? Did you also eyeball the gaskets to make sure you installed the correct ones as sometimes there's just a little difference in some. Sounds like it's sucking air somewhere like a gasket isn't sealing. The 28 squirter is a little small IMO and the pink cams aren't very aggressive. They shoot fuel all the way through the range but most of the time a cam that gives a quicker shot (as long as it's not so much to drown the engine) will work better. If it were me I'd start with a set of orange cams and a 32 squirter up front.

Even when the fuel mixture is right on plugs over time tend to get carbon fouled, especially when you have a nasty cam like yours that requires a richer mixture than normal. The only time you can really get a correct read on plugs is when you first install them and take it for a wide open run shutting it down right at the end of the run (don't allow it to idle) then pull over and pull them out and look at them. As for the correct heat range that's determined mostly by the compression ratio and indicated by the heated spot on the plug ground electrode. You really need to stick a new set of plugs in it and run it a little then pull them and read them. Here's a link to a page on reading plugs

http://www.dragstuff.com/techarticles/how-to-read-plugs.html
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Thanks a lot ,lots of great info I never knew....my compression is just over 10:1
 
Sorry I forgot to answer about taking the carb apart...it has the blue gaskets...they didn't rip/tear. I just put the carb back together cuz i felt they looked good and didn't have any new ones kicking around. Bad me???
 
340Duster247 said:
Sorry I forgot to answer about taking the carb apart...it has the blue gaskets...they didn't rip/tear. I just put the carb back together cuz i felt they looked good and didn't have any new ones kicking around. Bad me???
Click to expand...

They are touted as non-stick but not necessarily reusable. I have ran into cases where I was able to reuse them but sometimes their crushed down to the point they just don't seal up very well again. One thing you can do that helps is apply a thin film of chap stick, Burt's bees, etc on both sides of the gaskets so they come off easier and don't tear up. I've reused them 2 or 3 times doing it that way. Check everything over good for vacuum leaks and make sure the accelerator pump is working properly like Rob said. Shouldn't be any play in the accelerator pump when you bump the throttle. Should squirt immediately. Like I mentioned above it's a good possibility you'll have to go bigger with the squirter and with a more aggressive pump cam to completely solve the flat spot and make it perform it's best.
 
Thank you. The gaskets didn't even come off the main body side of the carb. I just removed the bowls and metering blocks. The accelerator pump does squirt right away but like I said I'm no carburetor jenius but have done my homework. The cam stuff gets confusing trying to figure out what cam works for what set up. I'll try orange and jump up in squirter.
Should I be worried about secondary squiriter size. It's a 31 now.


Haha makes me wanna bite the bullet and buy self learning efi
 
I'll try and take some videos of the engine shake and hesitation tomorrow if you boys wanna check in tomorrow night.
Might give you an idea what I'm up against
 
I had the same problem. Had an external balancer on the engine that was internally balanced. Quick $50 fix from TCI
 
340Duster247 said:
Thank you. The gaskets didn't even come off the main body side of the carb. I just removed the bowls and metering blocks. The accelerator pump does squirt right away but like I said I'm no carburetor jenius but have done my homework. The cam stuff gets confusing trying to figure out what cam works for what set up. I'll try orange and jump up in squirter.
Should I be worried about secondary squiriter size. It's a 31 now.


Haha makes me wanna bite the bullet and buy self learning efi
Click to expand...

Ok. You might need to go bigger on the secondary side too but for now leave the 31 in it. Get the primary's working correctly first then tune the secondary's. There is a lot to consider when choosing a cam. Took me a while to learn all the aspects and I'm sure there's still a good amount I don't know. I usually call up a good cam grinder (Bullet cams, Racer Brown, Lunati, Comp cams, etc) and talk it over with them and have my cams custom ground to the application. I know what generally works but their the experts and can recommend what's best.
 
When you say the idle mixture screws are out 1 turn, is that where it idles best? Slowly turn the idle mixture screws in until you hear it slow down, then turn ccw slowly and set them at the highest, smoothest rpm.
 
fishy68 said:
Ok. You might need to go bigger on the secondary side too but for now leave the 31 in it. Get the primary's working correctly first then tune the secondary's. There is a lot to consider when choosing a cam. Took me a while to learn all the aspects and I'm sure there's still a good amount I don't know. I usually call up a good cam grinder (Bullet cams, Racer Brown, Lunati, Comp cams, etc) and talk it over with them and have my cams custom ground to the application. I know what generally works but their the experts and can recommend what's best.
Click to expand...

Thanks a lot. But i was talking about carb pump cams.
Haha
 
did you go with adjustable rockers with the camshaft, a bent intake valve will cause engine shake and some times smooth out at high speed .
 
Switched out cam when we pulled the engine last month. Went with a lunati 60405. Engine still shakes pretty rough at idle. I checked engine mouts when engine was out and couldn't see anything wrong.
What engine mount are you boys running
 
Engine mounts do not cause an engine to shake. Although "something hitting" like a header beating against a T bar can certainly transmit vibration, etc.

Might be time to go back to basics

Has the carb got a problem, IE do both left and right side idle circuits work?

Do the idle screws have "good" effect and is there a definite "peak" on the adjustments?

Pull the carb off........are the throttle blades properly located in the idle transfer slots?

What is your initial timing and how did you decide on it?

Have you actually checked continuity on plug wires?

Don a dynamic cylinder balance test? That is, short out cylinders and compare RPM drop?

Run a cylinder leak down test?

Compression test?

=================================

Have you for absolute certain eliminated a balance problem? (I don't know what you have for slugs, crank, and rods..........so.......... ......... or converter, weights, flex, or balancer...................).
 
As far as engine cylinder test. The engine is bran spanking new again. And the compression tested ect. All good.
As far as timing my engine builders tech was bored and came over to help break it in. He gets paid to do this for side work, so I'm confident he knows his stuff. Initial is 18*,34 total. Runs hard and strong. Plugs read good. Maybe a lil rich on the porcelain.
Idle screws work. I'm about 7/8 out.(turn).
All wires/ plugs are good. Just checked that due to a different story when I pulled the engine.
Only other problem is engine is getting hot. Don't wanna get off topic but runs cool around 185-195. Until u get on her and just climbs to 200-220 and does not come down after. Stays hot. Even on highway
But that's another problem for another thread. I'm still getting this new engine dialed in 100% obviously. But was trying to get rid of this shake.
I have a big cowl hood and I can see the air cleaner at idle move 1" either direction. Sometimes worse then other times.
I've looked everywhere for a vacuum leak.
 
Post a video. Otherwise there's no way for anybody to know anything.
 
You sure the motor mounts are good ? Stock mounts are not great , broke 2 ( in 4 months ) before I changed to Shumcher poly loc ,mounts . Air cleaner should not be rocking 1" both directions
 
I agree with 67Dart that motor mounts do not cause an engine to shake. I've started engines (albeit they were stock engines) sitting on the ground with absolutely nothing holding them down and they didn't shake. Either it's just the big cam and things aren't tuned right or it wasn't balanced right.

BTW: that Lunati 60405 is a pretty darn healthy cam for a 340. You probably didn't change the idle much by switching to it. If you wanted a mellower idle you should have went with a cam about 2 sizes smaller like the 60403

Post a new video and we'll listen to it again. And this time post an under hood shot of the engine itself idling. We can tell a lot more if we actually see and hear it
 
Okay guys!!
Have a new set up. Internal balanced scat 408 stroker. Same heads. Lunati 60405 (degreed correctly).
AFR is 12.5-13 at idle. Checked for vacuum leaks everywhere with nothing.

Still shaking. Especially when decelerating back down to an idle (1200 rpm) shakes a lot.
Locked my timing out at 34. Still shakes at idle. Haven't driven it locked out yet.

Only thing I'm looking into now is if the damper is wrong.
I'm going insane trying to figure this out haha.
 
Not to point out the obvious, but are you sure there isn't something loose on the car itself? I'm thinking suspension/exhaust/mounts. A choppy idle can easily make a loose item into a serious shake. The off balance will just compound the problem and make the shaking seem a lot worse than it is. I would just start grabbing stuff and shaking it hard to see if anything is loose.
 
Worked on a mustang that had the exact same symptoms that you described. Had a slightly bent crankshaft flange that bolts to the converter. Took out a main bearing, but made great oil pressure and power. Only shaked at idle, smoothed out when the rpms got up. Was a really odd issue.
 
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