Transition Problem 1990 150HP Johnson

[Hoop1101]

Backstory: Just got this motor running this week (90' 150HP). Had a problem that it would run on the muffs, but not in gear in the water. I had "rebuilt" the carbs (which are from a 1976 200HP Johnson) the week before, but missed an important step. I didn't remove and clean the jets. Took them all apart, removed the jets this time with the proper tool and cleaned them well, noticing many blockages in them. Took it to the lake yesterday and it ran great, however I did not idle around much.

Took it to the lake today and now I noticed this problem: After idling for long periods (over 45 seconds), or turning the motor off, it will die when trying to accelerate. If I try to go past about 1/4 throttle it will bog down and die, like it is starving for fuel. Bumping the choke does not help. It will start up again immediately after. The only solution I found was to run at 1/4 throttle for about 30 seconds, and then it would transition fine without dying after that. I can even go back to idle and back to high speed with no problem UNTIL I idle for a long period.

FYI: I am running directly from a new 6 gallon test tank with new fittings, primer bulb, and hoses when this occurs.

EDIT: It also doesn't help by squeezing the primer bulb, which I think would rule out my next comment.

I was thinking maybe fuel pump(s), but that doesn't explain why it runs well at full throttle sometimes. I am lost as to what to check next. Thanks for the help everyone!

-Hoop1101-

 

[flyingscott]

What is your idle speed in gear. Did you clean the low speed orifices sounds like your idle is low or a partially plugged low speed orifice. It could also be your link and sync or the carbs themselves. Hard to be specific because you have 1976 carbs on a 1990 motor.

 

[emdsapmgr]

You did not mention which 150 engine you have. Makes a huge diff. Are you running a 1990 XP/GT 150 version? (the model # is a 150S) These 150S engines had huge carbs to support the extra hp that the GT/XP make. A 1990 XP/GT made 10% more hp than the hp numbers on the cowling-about 165 hp. Compare the difference for the prop rating to the 200 crank rating and the hp number differences gets smaller. The 200 hp was measured at the crank, so is 10% less than 200 hp. Maybe 180 crank hp. Your 200 carbs are very early carbs and don't have mid-jets which help in transition. In addition, it's possible that they are actually smaller than the XP/GT carbs. So, first thing is to determine the throat size of the carbs you are dealing with: Look at the front flange of the carbs. Cast into the front face of the carbs is the diameter of the throat of each carb. For instance, it is possible that the 200 carbs have a 1 1/4 (inch) throat size. It is also possible that the GT/XP carbs have a 1 3/8 (inch) cast into the front flange of the 150 carbs. If so, you've actually put smaller 200 carbs on a 150. Depending on what you find the throat size of your carbs are, you may actually be reducing the available hp by using the 200 carbs. The 1 3/8" carbs were always used on the big block 235 engines. Let us know what you have.

 

[Hoop1101]

Thanks for the help guys! I really appreciate it.

Idle speed is good, about 600RPM in gear. I did clean the low and high speed jets, and all surrounding passages, etc. It idles great in gear and runs great at high speed. Could setting the floats a bit off cause this?

The motor is a 150TXES. The carbs that came with the motor are 1-1/4 throat. The carbs on it now from the 200 are 1-5/16.

 

[sutor623]

Whats the model number on this motor? I had a similar issue where I had to give it tons of throttle in neutral during warmup EVERY time I started the engine. My issue ended up being warped plastic carbs (which I am guessing you do not have because of the retrofit) and also dirty calibration pockets in the throttle bodies. Many forget about these tiny orifices, but I ran carb cleaner and a welders tip cleaner through there and now she runs perfectly!!

Just read your comment about the carbs coming off the 200. Too many variables here!!! Changing the throat sizes will just add to the equation. You need to check your jetting. Did you pull the spark plugs and make sure you arent running lean?

 

[emdsapmgr]

Your engine is the base 150 hp unit. 150 prop hp. The carbs on the 200 are larger throated than the ones you took off the 150. The larger the throat, the more air/fuel you can get into the engine on each stroke. Just to reiterate, your original 150 carbs have a mid jet which helps in transition from idle to high speed. The 200 carbs don't. That could be part of the problem. You might be better off getting a set of 1 3/8" carbs from an XP/GT 150 from your model year. That would be the deal. You would notice the difference in the seat or your pants.

 

[Hoop1101]

Thanks guys. Sutor, thats right I do not have plastic carbs or bowls. I will pull the plugs today and take a look at them.

Emds, that makes sense. Thanks for the info on my motor. Those carbs from the GT sound great, but havent checked price and availability yet. I dont really have a problem going back to the stock carbs, I just wanted to gain a few more HP from the bigger throats. The weird things is that it does not happen all the time. It will transition fine EVERY time until it sits and idles. Any chance it could be a needle valve/float sticking closed in the carb? Or, like i said perhaps I didnt get the floats set just right. I have heard level with the base was how to adjust them or just a tiny bit higher.

-Hoop1101-

 

[sutor623]

Yep level with the base is the way to go, + or - 1/64". Could be float heights off but normally the bulb wouldnt get hard when priming the engine when it is level. Does sound like the engine is loading up at idle though seeing that it only acts up after idling for a while. Does the idle sounds smooth and ready to go, or does it stumble after idling for a bit?

 

[Hoop1101]

Hmm. The bulb does indeed get hard when priming. It does not sound like it is loading up when idling. Idle is smooth and goes from idle to 1/4 throttle without hesitation.

 

[emdsapmgr]

The high speed jets are stock in these carbs:

1976 200 .058 1 5/16" throat/venture Does not use mid-jets.
1990 base 150 .056 1 1/4" throat mid-jet size: .029
1990 XP/GT .065 mid-jet size .030

your 200 carbs have a larger throat. This lets more air and fuel pass, an is great for top end. Unfortunately, the larger venturi opening also decreases velocity through the carb-esp a low rpm's: so the hole shot suffers. I'm not sure just what throat size the XT/GT is. For sure it's 1 5/16" but could be 1 3/8"

The thing the 200 carb does not have is a mid-jet. The 1990 carbs supply tons of fuel through the main jet, but also supplys extra fuel through the intermediate jet. May be one reason the 200's don't run they way you'd expect.

When you get into changing carbs, it's more than just the carb. It's the throat size, the jet size and on the newer carbs, if there is a 3rd jet, mid-jet. It's complicated

I've swapped a lot of carbs and have a stash of jets in a box. Seems like when I swap carbs, it takes 2 or 3 different test runs with assorted jets before I get it dialed in.
You may find some swapping of jets may be of value. (despite the fact that these brass jets are $ 13 each.)

 

[Hoop1101]

Thanks, I continue to learn new things. Makes sense about the mid-jet. Is there any chance that using slightly larger low speed jets on the 200 carbs could help provide a bit more fuel for the transition? It currently has size 31 low speed jets.

 

[ondarvr]

Thanks, I continue to learn new things. Makes sense about the mid-jet. Is there any chance that using slightly larger low speed jets on the 200 carbs could help provide a bit more fuel for the transition? It currently has size 31 low speed jets.

It may run slightly better at midrange, but then terrible at idle.

I have a 1976 200, they are well below 200HP and were considered weak right from when they came out, a typical 150 could outrun one. I'd go back to stock and then look for a much newer set of carbs.

 

[emdsapmgr]

It was expecting a lot of a 149 cubic inch displacement engine to put out 200 hp. These old 200's had tons of hole shot grunt, but ran out of hp much over 5700. They made hole shot grunt from extremely high compression, and small venturi carbs. Look for the XP/GT carbs from 150 from 1990. While you are at it , get a set of 6 rubber intake filler blocks. Used on the 200 and 235 crossflows. Go inside the intake next to the reed boxes. Will yield 5-8 hp on a V6. Part number: 322722. This part is NLA, but you can still find them.