I need help with carb jetting for 150 johnson

[keefallan]

I have an '85 j150tlcos. It is a frankenstein motor that I purchased from a man in Atlanta{not knowing at the time). I just pulled the carbs off to give them a proper cleaning. I saw that my jets are not what my parts manual says I should have. Main jets are 60c or 65c depending on carb. manual says 55c. The other jets in the float bowl are 30 and the manual says 29. My idle bleed screws are mix/matched. two carbs have a 33 on one barrel and a 35 on the other. The bottom carb has 35's. The manual says 33. This motor has been bored. Is this a problem? Do I jet for a 150 or a 175? Iam going to install boyeson reeds also. Anyone experienced with jetting these things? Also, my carbs are 1 5/16.

Thanks.........Keith

 

[Dhadley]

Re: I need help with carb jetting for 150 johnson

The jets for that style carb stay with the carb regardless of which motor they're on (at stock recreational rpm). Use the parts catalog for the motor the carbs came on for proper jet numbers. Boring the cylinders has nothing to do with it.

 

[keefallan]

Re: I need help with carb jetting for 150 johnson

Thanks for the info. Where do I find the the #'s for the carb's. There are no labels or anything on the exterior of the carbs. Also,shouldn't the plastic float bowls be flat on the mating surface edge with the carb body? Two of the 3 appear warped(visibly). Maybe I should just look for a set of carbs!

 

[emdsapmgr]

Re: I need help with carb jetting for 150 johnson

Those larger carbs were probably not installed by the factory. Those 1 5/16" carbs were typically found on the 150S (XP/GT) or the flatback 175 models and yours is a base 150. They are all the same throat size, so it's hard to say why the jets are different. Perhaps they are a mixture of carbs from different year engines. I would think the engine might not run/idle well with that much variance in jet sizes from carb to carb. You may be able to determine if the carbs are a matched set by looking for carb numbers on the castings on each carb. It's always possible the prior owner rejetted one to compensate for carb bowl air leaks. The plastic float bowls installed at the factory are a real problem. They all warp over time and don't seal well when mated to the upper carb body. (fuel leaks.) Worse, it is possible for them to develop an air leak and run lean, possibly damaging the powerhead. I'd sort out the carb part number issues first, then decide to replace the bowls. If you order replacement carb bowls from Bombardier, the new ones will come cast aluminum. Regarding jetting, I'd be looking at the jet sizes found on an 85 150S model.

 

[keefallan]

Re: I need help with carb jetting for 150 johnson

Thanks for the great advice!. That's exactly what I'll do. After some research on my own, I also came to the hunch that they were carbs off a 150 gt/xp. They all have an 89 stamped in the casting. So, I guess they are a matched set with jacked-up jettings on the idle and main circuits.

Trying to figure this engine has been a nightmare! I will set the carbs up for it being an 85 motor. The best i can figure out is that the guy I bought it from put an 85 powerhead on 89 stuff. So, I'll set everything up as if its an 85 engine. That includes timing right? timing figures are different for those 2 years.

 

[emdsapmgr]

Re: I need help with carb jetting for 150 johnson

Depends on the heads that you are running. Check a factory parts list. If you have stock base 150 heads, set the timing at what the 1985 label on the spark lever indicates. If someone changed to higher compression heads, that's another story. You need to be careful. Some of the 150S XP/GT models recommended 30 degrees, which is only for the low comrpession bathtub heads. Would not hurt to run premium in it, either.

 

[keefallan]

Re: I need help with carb jetting for 150 johnson

I definately have the normal heads for the engine. Now, the next problem: my evinrude tells me to set timing according to the label on the cover of my motor. Well, I am not sure of the year of the cover if you know what I mean. So, what's the timing for an 85 150?

 

[emdsapmgr]

Re: I need help with carb jetting for 150 johnson

You may be able verify the year of the engine by checking the model number on the casting plug on the top of the block. The factory service manual for the specific year should have the timing information in section 1, under syncronization adjustments.

 

[keefallan]

Re: I need help with carb jetting for 150 johnson

Believe it or not, that's where I found the response " refer to the label on your engine" ! Can you believe that? My factory service manual for 1985 states max throttle timing settings for every motor except for the v6's! I can't believe it. Do you have any suggestions? One thing I don't want to do is burn a hole in a piston cause I've got it too far advanced, and then again, I want the most power out of this beast as I can get. DOHHHH!

Thanks again for your help by the way.

 

[emdsapmgr]

Re: I need help with carb jetting for 150 johnson

I checked an 85 factory manual and confirmed your comment. The manual refers to the label on the airbox cover for the timing. The heads on yours are the same as on the similar 86 base 150 model. The 86 service manual lists the timing for the base 150 at 32 degrees -+ 1 degree. You might want to consider running fuel that has an octane higher than the recommended 87.

 

[keefallan]

Re: I need help with carb jetting for 150 johnson

Thanks for all your help! That's what I'll set it to and run some better octane gas( I had been contemplating doing that anyways). I still haven't even done the 10 hr break-in yet!. I also got a great deal on a set of carbs off an 89 johnson 150. They look 20 times better than the ones that came on this engine. I'll just go thru them to clean them up and verify jetting! You have been a great help

Keith