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1999 70HP Johnson bogs down at higher RPM

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Botumfedr

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Bought the engine last fall and it ran like a banshee. Earlier this year had it out and it ran fine. Had a fuel feed problem due to a collapsed bulb and replaced the bulb, fuel water separator and a major part of the fuel lines-all fittings ck'd for air/fuel leaks . Engine runs well at lower speeds until you put the throttle to it and it will wind up for a short while then bog down and regain RPM for a short while. Will continue to do it while losing power until I back off on the throttle and reduce engine speed. Then everything is fine at lower RPM. I'm thinking clogged high speed jets in the carb and wondering if I am ready for a carb cleaning or rebuild. A rebuild seems the way to go if the the carbs are the problems as the rebuild kits are very cheap. Engine compression is 140-143PSI. Thoughts out there from some of you experts?
 
Have you checked your spark to make shure all cylinders are firing??cloged jets will definatly cause the problem you are describing!!My engine did the same thing,rebuilt my carbs and ran like a banshee as you call it.I would check my spark first.
 
i have been dealing with a 70 hp john/rude myself. not 99 but 01. weak timerbase, intermitten stator, good cDi box but it thought the motor was running hot (tan wire). all said and done idle was all the time a problem. sometimes good usually not and a couple of refuse to run. if your motor idles good in gear that says. comp is good and fire is also working, and fuel is close. you may be losing fire or fuel as rpms go up. the main jet is the biggest but not the last one to become plugged up. also an air leak anywhere in the fuel system would support an idle but not wot. the fuel pump witch failed to pump at idle but would pull a tube till the cows come home was $550.00. a primative vro no less, $15.00 later and some time back in the water again. also check vents on fuel tank(s). just my $.02 with no refunds
 
reveiwing the OP again sounds like running lean, if so you will burn one or more pistons. your rotten fuel hoses and primer ball are probably in the carbs. you may not even need kits. often times a goo remove will do
 
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Cisco, not experiencing any missing or loss of power that might be due to low spark or a misfire-fuel economy at lower speeds is good. Good compression in all three cylinders.

Going to ck the fuel pick up in the tank to see if it is constricted then work on the carbs. Will try and clear the HS jets if I can get to them w/o pulling the carbs. Trying not to screw up the linkage in the carbs if I can get to them. If not, I'll seek professional assistance. Talked with one mechanic and his first comment was to ck the fuel pump for pressure or vacuum. Anyone use this method to troubleshoot the fuel pump? Don't want to pay for a fuel pump ($350+) if it is not the real problem. Engine seems to run too well at all RPMs for fuel pump problem. Just experiencing a fuel starvation issue at higher RPM which bogs down and then recovers RPM. That doesn't sound like a bad fuel pump. Still working on it.
 
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