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Discussion Starter #1
The Tohatsu 25 will idle and run perfectly with the engine cover off but as soon as I put the cover on it begins to sputter. The air intake on the cover is not blocked in any way but for some reason seems not to be letting enough air in. Any ideas?
 

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The Tohatsu 25 will idle and run perfectly with the engine cover off but as soon as I put the cover on it begins to sputter. The air intake on the cover is not blocked in any way but for some reason seems not to be letting enough air in. Any ideas?
Maybe:

1. The cover is somehow pinching or crimping a fuel line

2. The cover is binding against the choke linkage

3. The cover is binding against a wire or electrical connection

If the sputtering is instantaneous it may be an electrical problem. If the float bowl is full it should run alright for 5 seconds or so before starving.

Look for "shiney" spots on any fuel line or any wires that are near the cover.

With the cover off will the motor pull maximum revs under load? If so, it is likely a chafing/crimping problem rather than an air starvation problem. Does the cover distort when closing it?

Did the problem come on gradually or all at once? Was there any work done just prior to the problem?

Check the mouth of the carb for any debris that may have been sucked in there

Paul T
 

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Good list BUT a fairly small exhaust leak will do this also
Very good!!, I forgot that one. We had a well & it was imperative to keep the lid wide open. Any exhaust gas blowback into the well would make the motor run rough. Check for any dis-colorization in the head gasket area & where the
power head mates with the lower unit.

Not sure if a leak would show up on an infra red heat gun?

Paul T
 

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Discussion Starter #5
Thanks for all the answers. No pinching of fuel or electrical lines that I can see. The problem arose pretty quickly. Had it running at home when I got it running for the season, but the cover was off. I thought about the choke being partially engaged but that seems Ok. Could the fuel mixture be too rich?1
 

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Thanks for all the answers. No pinching of fuel or electrical lines that I can see. The problem arose pretty quickly. Had it running at home when I got it running for the season, but the cover was off. I thought about the choke being partially engaged but that seems Ok. Could the fuel mixture be too rich?1

IIRC, since about the early 60’s, the motors I had had fixed high speed jets with only the low speed circuit adjustable. If it will pull max revs under load with the cover off the high speed jet is probably OK.

Possibly some debris has formed in the carb during the layover time, especially if you didn’t drain the carb before storage. You might try adjusting the low speed jet, although it may have a plastic cap on it. 1-1/2 turns out was where I used to start then richen it up to the point it starts to roughen up a bit, then back just enough to smooth it out

There can be both air bleeds in addition to fuel passages that can be partially plugged with fine debris. You might try dropping the float bowl, turn on the gas, & tickle the float up & down to clear any possible debris in the float valve.

Could be the cover makes just enough restriction in the air flow to effect it with a small debris restriction. If it has any kind of air filter or sound baffle, check those out. If there is no exhaust leak, my guess is that you may be in for a carb cleaning episode. Maybe try a 50% mix of gas & carb cleaner through it before pulling the carb?

Let us know what you find.

Paul T
 

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Discussion Starter #7
Well I was not able to figure it out myself. Took it the boat / engine to the local outboard shop. Turned out to be an electrical wire issue that only acted up when the engine cover was on. Sparkplug wire replaced and tied town away from the cover. Haven't put in water yet to confirm. Looks like points top Dabnis for a good diagnosis. Thanks for all the suggestions.
 

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Well I was not able to figure it out myself. Took it the boat / engine to the local outboard shop. Turned out to be an electrical wire issue that only acted up when the engine cover was on. Sparkplug wire replaced and tied town away from the cover. Haven't put in water yet to confirm. Looks like points top Dabnis for a good diagnosis. Thanks for all the suggestions.
You are welcome, thanks for the feedback. One can always learn from other's experiences.

Paul T
 

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Not knowing your model (2-stk, 4-stk carbed or EFI), can only speculate that you have an old 2-stroker with work ignition wires. But a common problem is exhaust ingestion.
 
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