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1978 6hp Surging at WOT. VIDEO ATTACHED.

J

jbone07

New member
I picked up a 1978 6hp which runs really well. The only issue is at WOT it will be running flawlessly and then all of a sudden, RPMs will drop a bit, then pick back up, then drop again. Seems very random. Please check out the video and let me know what you all think. Thanks in advance!

 
Starving for fuel.-----Check o-rings on fuel connecters.---Easy to replace those.----Check fuel line from motor to tank.----Check fuel pick up tube INSIDE the tank.----Newer plastic tanks are sometimes JUNK.----Older steel tanks are the best.----Also put new diaphragm in fuel pump.
 
racerone said:
Starving for fuel.-----Check o-rings on fuel connecters.---Easy to replace those.----Check fuel line from motor to tank.----Check fuel pick up tube INSIDE the tank.----Newer plastic tanks are sometimes JUNK.----Older steel tanks are the best.----Also put new diaphragm in fuel pump.
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Thanks and I will check all of that out!

Do you think this could possibly be a power pack issue?
 
I doubt it is a powerpack issue.------Lost spark makes for " instant " loss of power.----And " instant " regaining of power.----And do you understand what a powerpack is / does ?
 
racerone said:
I doubt it is a powerpack issue.------Lost spark makes for " instant " loss of power.----And " instant " regaining of power.----And do you understand what a powerpack is / does ?
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Thank you for the info. I guess I have/had an idea of what it does, but do not entirely understand all of its functions. I will focus more on the fuel side issue at first.

I pulled the fuel pump. Could this be an issue? Looks like it is torn out a bit?
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The diaphragm is available all day long.--Note---- the diaphragm for these pumps may not be listed for a 78 model.----That pump was first used in 1968 on 3 HP models.----Used on up to 25 HP models.----.----Used for over 30 years and diaphragm is listed on some of the newer motors!!-----Repair kit is available as well.-----I would never spring for a new pump !---Pieces of that gasket may be stuck in the pump check valves.-----That gasket may not be the issue, but it can be made.----Note----Just picked up 2 more 6 HP motors ( 67 and a 69 model ) at antique motor meet.----Both had new ignitions on them.----But the skills at many dealers / shops are lacking.----And the high cost of labor has made these wonderfully simple motors a near " throw it away " item.
 
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racerone said:
The diaphragm is available all day long.--Note---- the diaphragm for these pumps may not be listed for a 78 model.----That pump was first used in 1968 on 3 HP models.----Used on up to 25 HP models.----.----Used for over 30 years and diaphragm is listed on some of the newer motors!!-----Repair kit is available as well.-----I would never spring for a new pump !---Pieces of that gasket may be stuck in the pump check valves.-----That gasket may not be the issue, but it can be made.----Note----Just picked up 2 more 6 HP motors ( 67 and a 69 model ) at antique motor meet.----Both had new ignitions on them.----But the skills at many dealers / shops are lacking.----And the high cost of labor has made these wonderfully simple motors a near " throw it away " item.
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Please tell him which Sierra fuel pump rebuild kit to use....He needs the part number, not an ass whipping...
 
Just stop the attacks.-----If I post the part # the original poster will not learn how to find the parts himself !---These pumps were first used in 1968.-----And a version of it used as a vapor extraction pump on V-4 / V-6 60 degree loopers of up to 175 HP in 2005 model year..----Repair kits were all the same.-----And a factory repair kit has very exacting instructions.----Perhaps the original poster can find a dealer willing to help !
 
Unbelievable! People come here for help, not to hear the pedigree of a fuel pump without a clear path. I know these pumps very well. The kit number is 18-7823
 
Thank you both for the information, and sorry to stir things up. Lol

I really appreciate the part number Fitz. It has been ordered.
 
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