Twin 70's from the 70's

[John90290]

I am running twin 1977 Evinrude 70HP motors on my whaler. Great motors for 30 years, had one top end rebuilt 7 years ago including carbs, the other, just the carbs. Like I?ve said, they ran great, now this.

I run them for a while at 3500 (like 5 minutes) then lefty bogs, coughs, and stumbles. I thought it was the fuel pump so I switched our the one from the good engine, and put it on the bad one and it did not help. Put everything back as it was and now both have the same problem.

1.) Compression is ok 120-122 on both engines.
2.) Fuel pump is ok as I bypassed it and ran a new tank with new fuel a new hose and bulb directly to the carbs with a buddy pumping it while we ran the engine up to 4k in the slip, then she bogs, and stumbles.
3.) new coils
4.) new spark plugs, all gapped correctly, all with spark
5.) new fuel lines

BTW, the only way to get it to run well again is to pull the carbs, clean them out with carb cleaner and then put them back on, then they run for a while and bog and stumble.

Questions:

• Should I just rebuild each carb myself?
• Is it that hard to do?
• How do I sync them( or do I have to ) afterwards?
• Should I replace the floats as well?
• Could it be a power pack issue?

I?ve searched on the forum and it seems like it's the carbs but not sure. I hate pulling stuff apart as I fear I might be causing more problems. Any help would be appreciated.

Thanks guys.

 

[mikesea]

Re: Twin 70's from the 70's

I would suggest you rebuild the carbs,the only way to do it right is totally taking them apart and soaking them in a carb cleaner that can be bought at auto stores,after soaking,I like to soak for a half hr in soapy hot water,hose them off throughly ,blow them clean if you have compressed air ,or shake the parts a bit and then use some carb cleaner in spray can and shoot through all passags,if the floats ,needle seats look old replace them,also be sure the gaskets are re usable,but new kits are always a great insurance.If you dont have a good spin on water /fuel seperator get one,they are worth it,be sure to remove the filter often and drain into a clear jar enabling you to note any water or dirt,carbs are not hard to do,just give yourself ample room to lay out the parts,if your fuel pumps are old,its a good idea to rebuild them too,again not hard,basically just diaphrams and there are springs,so be careful,you do have more than one pump so you will have the ability to do one at a time,if you forget how to do it,just look at the next one,the newer fuels are playing havoc with some rubber and plastics,so you may have problems from the fuel,your engines are 30 plus yrs and parts do go bad in time,the rebuild kits are avail on this site and the prices seem very reasonable

 

[John90290]

Re: Twin 70's from the 70's

Thanks for the advice, that's exactly what i was thinking; take a step back, take my time and do it right.

Ordered the rebuild kits and plan to spend a couple of days with caustic chemicals in order to make those three little monsters shine and then at least i can feel comfortable that the carbs are not the problem.

I've read about sync them afterwards, seems a bit challenging. Not sure if i should sync them individually or keep them as one?


Thanks again for the above reply

 

[Silvertip]

Re: Twin 70's from the 70's

Link & Sync is an all inclusive process. It synchronizes carb opening with timing advance and ensures all carb butterflies close fully and at exactly the same time. You need a manual if you don't already have one. Follow it to the letter.

 

[tashasdaddy]

Re: Twin 70's from the 70's

if you miss a step, start over from the begininng,