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383 High RPM and backfire

69trojan

New member
"I purchased a 69 28'TRoja

"I purchased a 69 28'TRojan with intentions of bringing it back to life.......after a carb kit, rotor and distributer cap, thermostat, and some other minor things, the motor runs well in the slip. However, when I took it out on the water, I could only get 2000rpm, I backed off to 1000rpm for a few minutes, then tried to go back up and it started backfireing thru the carb. I'm really getting disgusted. I've been out about 1000.00 on a mechanic and no improvements. I've learned alot on this discussion board and I think I'll Try timing next. Any better ideas?"
 
"check to make sure the weight

"check to make sure the weights in the distributor are free & moving & the springs are in good shape, double check the firing order, condition of plug wires etc, then do the timing, what about the coil?, condition of the points?"
 
"You have replaced the distrib

"You have replaced the distributor cap and rotor, I assume with new parts not used?

Check for air leaks at carb. Water in fuel.

Replace the plug wires you may be getting cross firing or dropping a cylinder if you are only getting 2000 RPM. New plugs too if you havnt already."
 
"New plug wires, coil seems to

"New plug wires, coil seems to be fine, points look good. This may be a dumb question, but I'm still learning, how do I get to those weights and springs. I know where they are, I've just never actually had the distributor apart that far. Thanks for the quick response."
 
"Thanks, I will try all sugges

"Thanks, I will try all suggestions and let ya'll know what happens. By the way, my mechanic says its a 383, its a big block engine for sure, but I've hardly seen any posts concerning 383s here, most are 318. What do you think is up with that, I know these boats came with 318s?"
 
"That's the old Road Runne

"That's the old Road Runner engine!

Suggest you find another mechanic, one who knows how to check spark advance with a timing light.

Jeff"
 
Yeah....I've kinda lost fa

Yeah....I've kinda lost faith in the guy.....1000 bucks out of pocket with no results will do that to ya.....
 
"You do need to make sure the

"You do need to make sure the distributor advance mechanism is free and working.

If its a 383 and has the standard carb it is probably a Carter AFB 4bbl. If so the set up for opening the secondaries is governed by a counterweight and must be correctly setup for proper transition in opening up the secondaries.

My bet before you go chasing all over the place is that you have a problem with the carb leaning out due to either a leak caused by incorrect carb overhaul or assembly by your mechanic, or a problem in the way the secondaries are operating (or not) as you transition the 2000RPM + mark.

The fact that you can get it to rev out on the mooring but have problems when you go for a run seems to me to point to the secondaries in the carb as the engine manifold vacuum will be different under load.

Be nice if you could swap the carb out for one from a wrecker. Might get you boating quicker with less frustration."
 
"Thanks Craig,
I found two ba


"Thanks Craig,
I found two bad plug wires last night, so my plans are to replace them and take her out with a buddy so one of us can watch the carb, etc. I'll keep you posted. What should the points and plugs gap be. I've read on here some where that plugs should be gapped .05 over, is this true?

Curtis"
 
"More data: Last night I noti

"More data: Last night I noticed the butterfly valve is only opening 30-40% when the engine is as warm as its going to get. I've read enough to know thats not right, the secondary won't open up if that valve is not open all the way. Right?"
 
"The mechanically operated sec

"The mechanically operated secondaries (below the "flip over valve") should open 100 percent IF the choke is open. What you see looking down from above, the "flip over valve", opens as the air rushes in, acting like an accelerator pump. It too should open enough so the air flow is minimally restricted.


Jeff"
 
"Curtis, Are you refering to t

"Curtis, Are you refering to the primary or secondery bores here. The butterflies are at the very base of the carb throats.

In any case I think your idea of going for a run with a mate as indicated above is a good idea at this point, specially if hes got some engine knowledge.

Tell us how you get on. The feedback will be valuable info."
 
"Getting there....Bought a tim

"Getting there....Bought a timing light and found two cylinders not always firing(bad wires), and, two that were out of firing order. Able to get up to 3300rpm with no backfiring, intake manifold getting very hot around the base of the carb at high rpm,gauge reading OK , runs very smooth....amazing huh!!!! Won't plane off, but I think that may be the bulid up on the bottom. Can you install trim tabs on a boat like this? What should max rpm be on this motor?"
 
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