raz0rblade654

Hello all,

I finally got my ‘71 on the road! Driving around town is fine for what it is (270s @.050 cam and 365cc heads). It certainly isn’t a daily but it’s what i expected/wanted with these specs. The problem comes ONLY in 4th gear. It seems like the engine completely gives up. I’ve gone as far as going full throttle in 4th, and get NO response. Yet again, I’m at a complete loss. It’s carbureted, so fuel isn’t the issue. Spark is there, too. The weirdest thing is that it’s an intermittent issue. It’s an M23 from Autogear. Any ideas? Thanks!

-Sam

4-vettes

not a ton of information there. Rear gear?

raz0rblade654

3.36 gear that it came stock with. Everything rear of the trans is stock.

4-vettes

Well, your cam doesn't sound that big. Many of us on here run more cam without issues. Your heads I can only assume are factory heads. not 365cc's But rather 365 iron heads.
I am not riding along with you. but something isn't working under load.
Timing curve? Vac can Timing? When does it start to tip? When is it all in? What is your idle vacuum?
What do your plugs look like? White? Tan ? or pitch black?
Like I said, you haven't given us much information to go on.
Your rear gear sounds fine.

SFOcean

Might b something in the steering column shutting off the ignition intermittently when you put it into 4th?
Anyway, nice engine. Must be a 555 or larger to run that cam and heads.

raz0rblade654

The timing is tweaked by me +/- 7.5 degrees thanks to an MSD timing adjuster. It’s all in at around 3,500 RPM, and starts advancing at around 2,000. It’s mech advance, no vacuum. Regardless of timing, it still just gives out in 4th, whether i take 15° out or put 15° in! I’ll pull a plug soon and let you know what they look like. I figured a 272 at 0.050 is pretty big but i may be wrong . And the heads are true 365cc intake runners, Brodix Dragonslayers. I built this to START making power at high RPM’s, 5,500+.

raz0rblade654

All ignition wiring was redone from scratch. 6AL goes straight from the battery and aftermarket switch. It’s a 489 but will rev to 7k+ haha!

4-vettes

OK. Now where getting somewhere. At least we have some information on your engine.
Can't see why 4th gear makes any difference other than load.
maybe 3.36 is a bit tall for this engine.
Still, is it really Fat?? rich.
Not clear on exactly what it is doing in forth gear.

raz0rblade654

My guess is load? I was doing about 45-55 MPH today, under 2k RPM. I know big cams love RPM, but I don’t think it would struggle this much just to maintain a cruising speed. I adjusted the mixture screws (1,150 Dominator 4500) until idle was best. I don’t have a vacuum port on the intake (Edelbrock single plane) so I went by ear. Maybe I just NEED to keep it over 2,500-3,000 even during cruising for an engine like this? This is my first engine with a cam/build like this.

4-vettes

Certainly there is a vacuum port on that carb.
None the less adjusting the idle mixture screws does just that. Adjusts the mixture at idle.
There is a whole lot more to setting up that carb than just adjusting idle mixture.
Perhaps the best thing you can do if you have limited experience with jetting up a carb for a performance engine. Would be to find a dyno tuner with experience with your carburetor.
Get it dialed on a dyno. Then you'll be good to go.

raz0rblade654

I’ll take it to someone who knows more than me, I’m not too familiar with carb tuning so that sounds like a plan. Thanks for all the insight. I’ll let you know what ends up happening!

4-vettes

Best of luck.

Rescue Rogers

THat a lot of intake volume. What is your engine 383, 454, bigger? Whats your compression. You may not be getting enough draw through those ports at its like trying to pull a vacuum on a fire hose versus needing a garden hose. High rpm sucks harder than just above idle. You may have it spec'd for a nice race engine that you are trying to drive on the street and your carb just isnt seeing enough signal.

Take it out again, get it to bog, down shift or put it in nuetral and pop the throttle . If it isnt reving bring it up slowly to you get response then pop the throttle. If it revs then you have too much volume for your driving situation

derekderek

it is a 454 with top end and cam that belongs on a 550 or bigger. 10.5 cr. we tried to talk him out of some part choices...

Rescue Rogers

If he changes the heads he may be able to get some use out of it

Kevin_73

Check your fuel filter.

raz0rblade654

FINALLY! something so stupid of me to even do, but I was driving around with no air filter… AND no hood. I dont have the clearance for the stock hood, and my foolishness is to blame for no filter anyway, after putting a filter on, it ran great! It mustve been the surrounding air making some sort of turbulence, or resistance and not getting air into the carburetor! The filter prevents this (along with preventing the engine from being a dust vacuum!) Im really a clown yall

4-vettes

Well, At least you found the issue! Happy Motoring!