Problem with Tohatsu 30Hp 4 stoke

[RoeWalker]

I have a Tohatsu 2002 MFSA 30A 4 stroke 30HP outboad, that is giving me some problems. I bought it from a guy that had let it sit a few months and when I got it home it idled really rough and died when you throttled up in neutral or simply put it into reverse or forward. I pulled the carbs and did a quick (but admittedly not thorough) cleaning, replaced the gaskets, replaced the spark plugs, and replaced the ign coil/plugwires. I also mixed seafoam into the gas to see if it would help.

After all of that the starts up quick, idles strong and throttles up great when in neutral. Reverse idles good and throttles up but feels like maybe it could be stronger. Forward will allow you to barely throttle up then it chokes out, dies, and sometimes back fires. If you bring the throttle back down in time while in forward it will continue to idle. But sounds a little rough. Not as quiet as a 4 stroke ought to be.

So my questions are- If I perform a compression check what is the psi spec for compression? Also, should I remove all plugs when checking or only the plug in the cylinder I'm checking?

Final (and most important) question- What the heck do you think is going on here and what else should I be checking?

Thanks for your help!

 

[TOHATSU GURU]

Re: Problem with Tohatsu 30Hp 4 stoke

Correctly clean the carbs and do not worry about the compression number. Just make sure the number is the same across all three cylinders.

 

[RoeWalker]

Re: Problem with Tohatsu 30Hp 4 stoke

Thanks Guru! Do you recommend all plugs removed when I check compression? Just one plug out? Does it matter?
Also- I'm assuming a proper carb cleanout would be removing all rubber components unscrewing the jets and dipping in carb dip? That was my original plan but when I got home with the can of carb dip it warned against submerging plastic as the dip could break it down. Two of the carbs have plastic fittings for the fuel lines. Any thoughts or suggestions?

 

[TOHATSU GURU]

Re: Problem with Tohatsu 30Hp 4 stoke

It doesn't matter on the plugs...Just be consistent with them either in or out. The plastic on the carbs will not be damaged by a three hour or four hour dip.

 

[RoeWalker]

Re: Problem with Tohatsu 30Hp 4 stoke

Compression =
top- 98
middle-112
bottom- 115

 

[Sea Rider]

Re: Problem with Tohatsu 30Hp 4 stoke

Top is on the wear limit compared to middle and bottom cylinders. Probably not an issue with current problems you`re experiencing already.

Happy Boating

 

[TOHATSU GURU]

Re: Problem with Tohatsu 30Hp 4 stoke

Compression =
top- 98
middle-112
bottom- 115

That's enough of a difference to warrant checking into why. Run the engine for around 15 minutes and then check again. If you still have the same difference it needs help.

 

[RoeWalker]

Re: Problem with Tohatsu 30Hp 4 stoke

OK. Carbs are apart and soaking. Now for a really stupid question. This motor has 3 carbs and in each bowl a small screw holds the float pin in place. I didn't pay attn to how tight that screw was when I removed it. But I did notice that the looser the screw the more range of motion in the bowl. Is there a rule of thumb for how tight this screw should be?

 

[TOHATSU GURU]

Re: Problem with Tohatsu 30Hp 4 stoke

Tight...If it is down tight there is no range of motion on it.

 

[RoeWalker]

Re: Problem with Tohatsu 30Hp 4 stoke

So I want the screw very tight so the float doesnt move?

 

[greg daigle]

Re: Problem with Tohatsu 30Hp 4 stoke

yes tighten screw.and blow compressed air through carb jets and air holes

 

[pvanv]

Re: Problem with Tohatsu 30Hp 4 stoke

So I want the screw very tight so the float doesnt move?

If the float does not move with the screw tight, something is seriously wrong. The screw just retains the float hinge pin. The pin must be seated correctly, and retained by the screw. Then the float moves on that pin. Vertically only. When down, fuel fills the bowl. When up, fuel flow stops filling the bowl. As the bowl fuel is consumed, the float lowers, allowing fuel to refill the bowl. Carbs 101. If this topic seems daunting, see your local dealer for assistance.

 

[RoeWalker]

Re: Problem with Tohatsu 30Hp 4 stoke

I didn't ask that second question very well. I noticed that the tighter the screw the less range of motion in the float. but its back together now and going to put in the water today. Will let you guys know what happens.

Thanks for all of your help!

 

[RoeWalker]

Re: Problem with Tohatsu 30Hp 4 stoke

Well...I spent yesterday evening thoroughly cleaning the carbs and I put the boat in the water today. I decided to throttle up while on the trailer (backed into the lake) so that I wouldn't have to paddle to shore if I had problems. The motor sounded great in neutral. Its a 4 stroke so it had that nice smooth sewing machine sound going. Reverse sounded good as well. When I engaged forward it performed much better than before but still wanted to bog down and backfire when I throttled up. However, it was waaay better than before so I went ahead and launched. Off the trailer the boat felt good. It did delay a couple times on the the throttle, but it didn't bog down and didn't back fire. When I put it back on the trailer and throttled up to push the boat the last few inches into place on the throttle it bogged down and backfired again. I checked the compression while warmed up and all three cylinders are between 115-120.
The carb was definetley dirty and some of the nozzles clogged so I expected improved performance but I really expected the cleaning to solve the problem. I guess its possible I still missed something on the carbs, but other than that not sure what to check next. Any additional advice is appreciated.

 

[pvanv]

Re: Problem with Tohatsu 30Hp 4 stoke

Of course, carb sync could be off. But my bet is that you need to go after the carbs again:

1. Complete disassembly, including jets and emulsion tube nozzles.
2. 4-hour soak of all non-rubber bits in real carb dip.
3. Liberal spray-out of all passages with generic carb spray. Use at least one whole 12-oz. can.
4. When reassembling, verify float height.
5. When reattaching, verify idle sync. and then adjust warm idle.

Popping through the intake is a sign of a lean condition, i.e. still some varnishing in the narrow carb passages.

 

[RoeWalker]

Re: Problem with Tohatsu 30Hp 4 stoke

Thanks pvanv. I'm looking at an online diagram and don't see "emulsion tube nozzles" I'm sure I'm familiar with what it looks like, but I'm completely self taught through trial and error, online advice, and repair manuals so often times I'm familiar with the parts and operation, but I just don't know the proper name-please forgive my ignorance. I pulled the two jets and cleaned thoroughly after dip with carb cleaner and compressed air (I think they are called fast and slow) one is covered with a screw and the other with a rubber plug.
Questions-
When you say emulsion tube nozzles, what are you refering to?
How do I verify float height? Whats my reference for the correct height?
What are the steps to verify idle sync and adjusting the warm idle?
I'm using Gunk "carburetor parts cleaner complete kit Gunk Details Would you consider this "real carb dip?
Sounds like its time to invest in the factory service manual. Is there an online resource for this manual or do I have to walk in to a dealer?

Thanks again for all of your help. I'm learning a lot as I go and hopefully I'll be able to pass it forward .

 

[RoeWalker]

Re: Problem with Tohatsu 30Hp 4 stoke

Scrap question one. I googled it and now know the correct name for the emulsion tubes. They were removed and cleaned.

 

[pvanv]

Re: Problem with Tohatsu 30Hp 4 stoke

It sure wouldn't hurt to get 003-21053-0, SERVICE MANUAL MFS25A/30A, $40.00, from any dealer (including several forum members)... even me. Skip the eftermarket manuals -- they are too general to be of much use. The Factory manuals are copyrighted, so they are not available for free download.

1- The nozzles are susceptible to "coronary artery plaque buildup", so they need to be completely clean -- especially the tiny holes through the sides.
2- When you hold the carb inverted, the float should be parallel to the carb casting.
3- You need each carb throttle plate to be exactly in unison with the others, and the pilot screws must be at exactly the same flow. That's synchronizing the carbs. There are several methods to accomplish that -- mechanical, or, ideally, by a vacuum gauge test. Since the MFS30A carbs have plugs blocking access to the pilot screws, they *should* still be OK.
4- After fully warmed up, attach a good shop tack, and verify the idle RPM in N, as well as the troll RPM in F. Adjust the idle stop screw (on the lower carb -- #3) to adjust.
5- That cleaner should be fine. I think we have some in the shop. It will soften the organic varnishing in the hidden passages. Then you will want to flush the softened gunky stuff out. Air is OK, but a solid stream of spray cleaner seems to be more effective.

Multi-carb setups are fuel efficient and responsive to the throttle, but do require some patience setting them up correctly. If none of the adjustments have been disturbed, you are probably OK with sync. Those carbs have accelerator pumps (plungers) that must be spotlessly clean in order to enrichen the mix when throttling up in brisk acceleration. If they are sluggish or blocked, you can get popping through the intake.

As always, confirm that you are not over-full with oil... not even a drop. 3/4 on the dipstick (on an older motor) is fine.

 

[RoeWalker]

Re: Problem with Tohatsu 30Hp 4 stoke

Thanks guys. Filled the bowl and cylinders with Seafoam and let it sit for 2 days then took it back on the water today. It smoked a little at first and was still sluggish when throttling. But after running it for about 30 minutes and multiple start and stop and start again to plane it seems to be running normal. Before I started this process it would back fire and bog down when trying to push the boat all the way onto the trailer. Today it did great and didn't miss a beat when I loaded up. Still feels like it may do a little better if I had someone sync the carbs, and the compression is still weird (90-90-110) but I'm pretty happy with the result. Thanks to all of you for your help!

 

[pvanv]

Re: Problem with Tohatsu 30Hp 4 stoke

Sounds like you have success. Cool. Now remember to faithfully run the carbs dry at the end of the day (or drain them) if you will not be running for more than a week. That will reduce the varnish buildup.