Johnson 70hp 88 bad holeshot

"I cant make a ski start anymo

"I cant make a ski start anymore. The motor bogs down. If I ease the throttle gradually it is possible to reach approx 3000rpm, suddenly, it will accelerate very quickly as before. In this weak interval using the switch key (priming) will improve signifficantly. Using the primer bulb though will do nothing.
This has happened after a carb clean due to bad idling. Now the idling is fine, but I got this new problem. WOT is also very good.
The carb linkage and cam is adjusted. Compression is 120 psi on all 3 cyls. I cannot really tell the strength of the spark because of sunlight and primitive conditions at sea, but it really seems to work at idle and WOT
What went wrong?
Robert"

richen the idle mixture slight

richen the idle mixture slightly per carb

Did you do a link & sync a

Did you do a link & sync after removing the carb linkage? (recheck the timing linkage setting with the carb linkage setting) Timing could be off from carb setting.
This is taking for granted that you did everything correct it the carbs and they have no problems.
It's not a good idea to expect that nothing has changed and you have the linkage back in the same place it was before you started. It doesn't take much for the alignment of the linkage to be off.
Try as Beck said but check the timing and carb throttle valve settings before you do so you know it is correct.
If the timing is off it can cause major problems in your money clip depending on how much it is off and what damage it does.

"Thanks for your answers becke

"Thanks for your answers beckerjs and charli.

Unfortunately the idle jets are fixed. Idle is adjusted by changing the timing base stop screw.

I also adjusted the carb linkage and cam after the reassembly of the carbs.
(I checked that the timer base isnt stuck.)

Improving by priming (pushing the key switch), makes me think it is fuel related.

The timing has not been moved, and performance in low and high rpms is good, the mid range is bad.
Any other suggestions appreciated.

Robert"

It seems ast You are haveing t

It seems ast You are haveing trouble getting the main jets 'started'. Normally this may be caused by two factores:
1: Lack of vacum in the air silenser box = bad gaskets.
2: Too low float setting in the carbs after rebuild.

"Thanks Morten.
I think that

"Thanks Morten.
I think that you are right about getting the main jets started.

About the gasket in the air silencer: Is the air silencer really "tuned" for a certain vacuum level? Isnt a minor leak through the gasket neglectable compared to the inlet opening in the silencer?
By the way the gasket seems to partly plug a hole in the carb flange. Could a worn/damaged gasket make a faulty vacuum in this hole?


About float setting: I usually check the float setting to horisontal when holding upside down, but im beginning to wonder if I assembled the the float in a way that it sticks in an almost closed position (enough for idling), and when it gets the "priming kick" releases fully to keep WOT.
I will disassemble once more and check your suggestions.
Robert"

"The 'silencer' partly

"The 'silencer' partly acts as Your acc pump. The carbs on the twp strokes have no such device, insted they use the 'vacum' created in the silencer to 'suck' extra amount of fuel. If the float level is too low (fuel level in carb), You need more vacum to lift up the fuel, and if the gaskets are leaking, You may not manage to get the jets started until the air flow speed through the carb venturi gets high enough to create needed vacum to the main jet. By pulsing the primer/choke additional fuel is given like an acc pump to get that extra needed which is normally obtained by the extra vacum. Some sort of 'manual' MAP sensor in an injection engine."

"Thanks Morten, you are amazin

"Thanks Morten, you are amazing.
I dissaembled the carbs once more. I found that the silencer gasket had swollen and completely had covered the hole in the top of the carb inlet flange. In that hole is a brass jet that probably is some kind of mid speed jet, it has connection to the same chamber as the idle supply. Perhaps that brass nozzle is supposed to balance the vacuum from the carb inlet throat for the fuel feeding?
Anyway I cut the gasket to free the hole, and I cleaned the carbs once more, adjusted the linkage, and went for a test run. A great improvement, but I cannot move the lever to WOT in less than a second, but maybe this is normal.
I will get new gaskets for even further improvement.
By the way, there were no sticking float valves.
I noticed that the revs should be approx 1800rpm before the lever can instantly be moved to full, without bogging. I guess 1800rpm creates enough vacuum to draw sufficient amount of fuel.

Would a slight increasing of the clearence between the cam and roller be beneficial, revving up slightly before the throttle plates open, and thereby getting a vacuum to draw enough fuel for accelerating (simulated acc.pump)? I might try tomorrow.

Thanks for great help and understanding.
Robert"

"I just tried to increase the

"I just tried to increase the clearence between the cam and roller. It didnt change much, but I really think it is acceptable as it is (small hesitation if lever is moved very quickly to full). I will also change the gasket to further improve the vacuum for a faster reaction.

Robert"

As a'last' adjustment

As a'last' adjustment I would like You to get a can of OMC/BRP 'Engine Tuner' (or equivalent) and give the engine a good treatment. If carbon build up in the exhaust system it may be difficult for the engine to 'breethe' properly ( too high back pressure).

"Thanks, Morten.
Robert"

"Thanks, Morten.
Robert"

"Last update for this season.

"Last update for this season.

Unfortunately I have'nt improved much. In a moment of positive mood I thought I did it.
The "Engine tuner" didn't work. A quick push on the primer will "release" the high speed.
I got a tip though: The gasket inside the float chamber might be leaking (circular rubber gasket). I replaced the gaskets for all carbs, but I will not get the answer until next season, as the boat is now on land. The old gaskets were quite compressed, so maybe new gaskets will work.

Any opinions if I'm on the right track?

Robert"