1956 big twin will not rpm up

R

ROACHCATCHER

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Dec 23, 2009
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just restored a 1956 30 hp evinrude big twin, new coil, water pump plugs etc....
motor starts and idle great, but when i give it the gas, it does not rpm up under load, i checked all i know too, does anyone have any thoughts???

i have it on a 16 ft jon boat, it just will not pick up rpm's and or speed..
tried all adjustments

help
 
A

a70eliminator

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Re: 1956 big twin will not rpm up

I don't know exactly how the timing advance happens on your engine, but most have a link to the distributor from the carb, and distributor advance relation to throttle position (link-n-sync) adjustment is very important to make power.
 
tashasdaddy

tashasdaddy

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Re: 1956 big twin will not rpm up

have you check compression and spark? carb adjustments. see the TOP SECRET FILE. 1st thread in this forum.
 
bktheking

bktheking

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Re: 1956 big twin will not rpm up

Sounds like the typical spark on only one cylinder problem. Yes they idle but won't rev worth a damn. Check to make sure you are getting spark on BOTH cylinders and good spark, sounds like you have a points/coil issue/plug or wire issue. Throw a timing light on each wire to check and/or a spark tester.
 
bktheking

bktheking

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Re: 1956 big twin will not rpm up

The other would be not enough fuel getting to the carb high speed side, high speed circuit in the carb dirty, does adjusting the high speed jet have any effect?
 
T

tmcalavy

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Re: 1956 big twin will not rpm up

Did you take the carb off and clean it in the restore? Is the carb butterly hooked up correctly to the throttle advance? The carb butterfly should open slowly and smoothly all the way as you advance the throttle from slow to fast. Check each of the things we've mentioned systematically and you'll find the problem. As already said, might be a spark problem. If the carb is squeaky clean make sure the high and low speed adjustments are at baseline, then adjust as mentioned in the TOP SECRET file.
 
F

F_R

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Re: 1956 big twin will not rpm up

I agree with the running on one cylinder theory. At least you should eliminate that possibility before going off looking for something else.

Remove and ground one spark plug wire and see how it then runs. Then do the same thing with the other one. Power loss should be equal in both tests. If not equal, it is usually an ignition problem. But can also be a mechanical problem. You Have checked the compression, haven't you?

I seriously doubt it is a carburetor problem. But could be the linkage as suggested. That motor has a "cruise" throttle and must be set up by the book.
 
samo_ott

samo_ott

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Re: 1956 big twin will not rpm up

It could be as easy as a high speed needle adjustment. Any engine will run like crap if it's outa whack.
 
kbait

kbait

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2,449
Re: 1956 big twin will not rpm up

Compression. Spark. Check carb link-up. Should run if fuel side is correct. Clogged/mis-set, or leaky packing in high speed needle/jet can explain symptoms once Compression and Spark are ensured.
 
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