got a question on a 135hp

[firefighter45]

I have a johnson 1975 135hp that we cant get to do more than about 4000 RPMs at wide open throttle. We have rebuilt several motors and have never had this problem before. There are 2 plates in the exhaust housing that we found in it when we torn it down we think are some type of baffle. Are these suppose to be in it or could this be giving us our problem. Every manual we have seen doesn't give these parts in the parts layout. We have tried everything we could think of so far and nothing seems to help. It is on a 18ft. Cajun fish-n-ski 1988 model boat if that helps. Also has tilt and trim. Trimmed out it gains about 250 RPMs. Motor runs like a new one just cant get the RPMs up.

 

[HighTrim]

Re: got a question on a 135hp

Welcome to iboats.

IF she is set up properly on the boat, and have proper distribution, have you ensured that she is firing on all cylinders? What is the current prop size?

 

[firefighter45]

Re: got a question on a 135hp

It is firing great on all cylinders and setup is fine. It has a 19 pitch prop we have tried three other props with no change. are we over looking something?

 

[Ganis]

Re: got a question on a 135hp

I'm having the same problem with a '79 150, just rebuilt. Gone through everything, spark, compression, fuel, timing. I've given up on trying to figure it out and taken to my mechanic, he's thinking it's some type of timing problem. I will let you know what he finds out, but it may be a week before he can get to it.

 

[firefighter45]

Re: got a question on a 135hp

can anyone tell me what the plates in the exhaust housing are for and if I need them or could they be restricting the engine from getting more RPMs?

 

[emdsapmgr]

Re: got a question on a 135hp

Hard to tell just what the plate are you are referring to. Perhaps you could attach a picture to your next post. This engine does have a high performance exhaust bubble on the back. The exhaust cavity on that 135 engine will have two exhaust filler blocks. Each should be bolted over the exhaust ports and will mate up to the inner exhaust cover on the back of the engine. These parts are considered part of the block and are not usually shown on any parts list.

 

[ezeke]

Re: got a question on a 135hp

The exhaust filler blocks will burn out over time, especially if the engine is run on high octane fuel.

You can run without the filler blocks, but the sound will be a little different. Just be sure that the gaskets on the exhaust covers are sealed well.

I don't recall if the exhaust filler blocks used on the later V4 models will fit or not - part #0392000

 

[fast6]

Re: got a question on a 135hp

I have the same motor on a 17.5' crestliner tri-hull. I run a 13x17 prop and it spins up to 5200 rpm. My 13x19 cupped prop will only spin to 4200-4500.

 

[emdsapmgr]

Re: got a question on a 135hp

Probably not an issue, but you might want the double check? I'm assuming that you checked to make sure the carb butterflys are opening all the way at full throttle after you reinstalled the engine.

 

[firefighter45]

Re: got a question on a 135hp

Do the exhaust filler plates restrict the motor at all or is there another reason for them?


I am gonna try another prop shortly just to see if thats the problem. but will \I be loosing any speed or will the extra RPMs help in that area?

 

[emdsapmgr]

Re: got a question on a 135hp

The exhaust filler blocks are part of the bubble back exhaust system and are found on the high performance (higher hp) models. That system is designed to improve performance, not restrict it.