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Discussion Starter · #1 ·
My 4hp yamaha f4a outboard will fire up with the choke out fine, once it is running it is not very responsive with the throttle and will rev up uncontrollably and then when the choke is pushed in it will rev up uncontrollably even more so and then stall.

Does anyone know the potential problems? It has not been properly run for many years (only me messing around with it) it has had fresh fuel. Is a dirty carburettor the only potential problem?

Any help would be very very much appreciated.
 

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Not familiar with that specific motor, but many small OBs have a roller/cam linkgage to the actual carb throttle arm. This roller rides on a cam which advances with the magneto. In other words, when you manually increase throttle, it's advancing the mag pickup in relationship to the flywheel, and the cam is pushing the carb throttle to match. It could be a simple case of gummy linkage, so when it gets pushed open it tends to stick. Find the cam/roller and try pushing it to open, then let your finger slip off of it, and it should snap right back up against the cam on the magneto.I would start by looking at the throttle linkage and carb throat. Disconnect the fuel, and if it has a kill switch leave it in the no-run position. Use spray carburetor cleaner throttle lever where it attaces to the , while you're operating the throttle lever directly with your finger (usually just takes a downward push). Clean things up and check it out.
 

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Discussion Starter · #3 ·
Thanks for your reply, however, I'm unfamiliar with some of the terminology that you have used (apologies).

I can see two things that can alter the carburettor. The throttle cable and the choke arm. Are you saying to just check whether these are both springing back as they should and that they are not gummed up?
 

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Discussion Starter · #5 ·
Thanks Paul, it seems like mine has a different problem than the 2 stroke. I don't know if I forgot to mention that Mine is a 4-stroke also mine will not ever run smoothly and will rev-up and stall when the choke is pushed in/ rev up un controllably when the choke is out.

Seems like fully cleaning the carb is the best option, any other ideas of what it might be?

Thanks,
James
 

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Thanks Paul, it seems like mine has a different problem than the 2 stroke. I don't know if I forgot to mention that Mine is a 4-stroke also mine will not ever run smoothly and will rev-up and stall when the choke is pushed in/ rev up un controllably when the choke is out.

Seems like fully cleaning the carb is the best option, any other ideas of what it might be?

Thanks,
James
Both2 & 4 strokes can suffer from fuel starvation problems in similar manners.
Assuming your ignition system is sound, it sounds like you may have a severe air leak, possibly along with fuel, restriction problems. Suggest you check/tighten the carb mounting bolts, not too tight, check all hose clamps & fittings & make sure the tank is venting properly. Try running it with the fill cap loosened or off. And all the other stuff mentioned in the other post. The linkage thing is also a possibility, but unless damaged by impact or over stressed, or loose connectors, not much has ever happened to me with the 10
outboards I have owned.

Paul T

My guess is that that there is debris in some/all parts of the carb
 

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Thanks for your reply, however, I'm unfamiliar with some of the terminology that you have used (apologies).

I can see two things that can alter the carburettor. The throttle cable and the choke arm. Are you saying to just check whether these are both springing back as they should and that they are not gummed up?
I'm having trouble finding a good diagram or picture of your model, to show you what I'm talking about. Could you remove the cover, take a picture and post it?
 

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Paul, I have checked all the carburettor/hoses and they all seem good, can the symptoms I have described not be explained by a dirty carburettor alone?
Could be, although the surging thing has me puzzled. Could be debris floating around, then being sucked up into a jet or passageway, & then being released again? Before taking the carb off, try dropping the float bowl, turn the gas on, & work the float up & down to flow fuel through the float valve. If there is any debris in the bowl, I would suggest cleaning the carb.

I have no experience with your particular engine/carb but suggest you bring the carb home, spread out a large towel, take it apart in sequence, from left to right & re-assemble in reverse order. Be careful of possible check valves, balls with springs behind them, or other loose parts when blowing things out with compressed air. Taking pictures while dis-assembling may help later.

Go slow, take your time, & tread lightly. If you tear a gasket or it looks bad, Yamaha no doubt sells a re-build kit, with new gaskets & o rings, probably a good thing to have before starting.

Or, just take the carb to a shop. :D

Paul T
 
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