OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Engines Questions On Briggs & Stratton Engines Briggs and Stratton 91202 Running Rich

Hi, I wonder if anyone could help me!

I have a Rover 45 with Briggs and Stratton engine (91202 -1371 E1) which runs very rich, just got it recently. It starts and runs fine but it is smoky (black smoke, I am pretty certain it is not blue). I have attached a couple of pictures of the main jet which is screwed in all the way.

I also have a Scott Bonnar 45 which also has a Briggs and Stratton engine (80202 2324 01) the main jet on the Scotty has a screw with a spring that allows you to adjust the mixture. The rover has a very similar set up but has no spring and is screwed in all the way. I have the parts diagram for both engines and I am guessing that I can�t adjust the mixture on the Rover

So my question is this; should I be able to adjust the mixture on the Rover the same way I do on the Scotty, or is there something else I should be doing?

I can't seem to add an image I will try and figure it out and load them.

Many thanks

Alistair

Hi adeas, and welcome back to the forum.
Grumpy is our resident Briggs guru, and I'm sure he will chime in here and give you some advice on your carby problem.

Hi adeas, that carburetor is supposed to have adjustable idle mixture, but it seems the previous tenant has thrown away the spring and screwed it in hard to try to suppress the symptoms of a malfunction which was making it run extremely rich. Because it is intended to adjust only the idle mixture, not the main mixture, his efforts were presumably fruitless - though he may have prevented it from idling, and also damaged the adjustment needle and its seat.

Here is the operator's manual for the Rover 45 engine:
http://bsintek.basco.com/BriggsDocumentDisplay/flmvtLX-nfBhU7y.pdf

Here is the Illustrated Parts List for the same engine:
http://bsintek.basco.com/BriggsDocumentDisplay/18jsBLXBnfBhU7y.pdf

The carburetor is a Pulsa-Jet - you can see an exploded view of it on Page 5 of the Illustrated Parts List.

The usual cause of extremely rich mixture on old Briggs engines, is a blocked air filter element. I suggest you run a brief test: remove the element from the air filter, and inspect it for dirt build-up. Run the engine briefly without the element fitted, and see if the exhaust smoke is eliminated. Do not continue to run it without the filter: this would allow dirty air to enter the engine, and wear it out. If the underlying problem is just a dirty filter you will need to buy a new one and fit it. We can then talk about how to deal with the butchered idle mixture adjustment. However if the black smoke still occurs with the filter element removed, we will have to discuss a carburetor overhaul.

Hi Grumpy, and thank you for the reply.

I put a new air filter in this morning and ran the engine for about half an hour and it is still running rich but certainly not as bad as it was so that's good.

With regard to the idle adjustment I was thinking that was controlled by parts 149 (1149 on the picture)and 689 which are intact and functioning OK.

Now I am a bit confused! The jet that I have circled in the pictures I thought was the main fuel mixture jet (Part 147 on the parts list)but you are saying it adjusts the idle mixture which is now beginning to make sense because it does idle fast, much faster than my Scotty.

Does that jet(147)have a spring and is it part 692?

Cheers

Alistair

We are having some communication problems I think. By my reading of the diagram on Page 5, Item 147 is a fixed jet, where Item 173 is an adjustable needle. Here is the page from the technical manual that hopefully describes the carburetor:


Your engine is a 91200 (the final 2 in 91202 just tells us it has a rewind starter.) Now, you haven't posted the Code for your engine (the set of numbers stamped on the cowl, right after the Model and Trim which you posted). The Code tells us its date of manufacture. However, the diagram above says that is the description of the carburetor for a 91200. The non-emissions version has an adjustable idle mixture screw, and is applicable only to "Current Version", in diagram A. That whole series of carburetors does not have an adjustable main mixture screw, though an earlier series, fitted to vertical crankshaft engines, did. A pilot jet is an idle jet, and the assembly diagram is telling us that your engine will either have Item 147, a fixed pilot jet, if it is an emissions carburetor, or Item 173, an adjustable idle jet, if it is non-emissions. Yours has an adjustable idle mixture screw, so it is the type marked [2], in the first diagram in the tech manual.

Item 692 is a detent spring, used for clicking into a recess to hold a control in a specific position. I don't know where it fits on the carburetor but I doubt it is relevant at this point.

If we can get onto the same page, adeas, the next step will be to verify that the choke is opening completely. If the linkage between the choke lever on the control panel and the rotary choke butterfly is bent, the choke will only open part of the way, resulting in rich mixture.

Hi Grumpy, Thank you for your time with this....

Code is 0203143A

I've checked the Choke and it is opening fully

I've also attached a picture of the jet.

Thanks

Alistair

Can you post a picture of where it screws in please? It sounds as if it is an emissions carburetor, and it is quite correct for it to be fully screwed in, because the idle mixture is not adjustable.

Up to now I've expected to find that your engine was made sometime in the 1980s, which is why I've been accepting the theory that it had adjustable idle mixture. Your engine was actually made on 14 March, 2002. I thought Rover 45s were out of production by then, which would make it a replacement engine, but Deejay is the reel mower guy, I'm sure he'll put me right as required.

Hi, yes I am beginning to think that it is not adjustable after reading the details you have provided.

I do believe that the new air filter did make a difference even although the old one "looked" OK to me, just shows!

This is where it screws in ... circled in RED

Hi to Grumpy and adeas,
I believe that Rover were still manufacturing the Rover 45 as late as early 2008....I know that they were still manufacturing spare parts at that time.

Thanks Deejay - that means we just have an ordinary emissions Pulsa-Jet there, with no mystery beyond why it is running rich. Since it has been established that the air filter is OK and the choke is wide open, it sounds as if it will probably be necessary to remove and open the carburetor to take a look at the main jet. However, a question first: adeas, was the slot on the pilot jet already damaged when you got the mower? If it was, we still need to be on the lookout for foul play by the previous owner. This could include interference with the calibrated holes behind the jet.

"Was the slot on the Pilot Jet already damaged", I don't really understand the question. Do you mean the screwdriver slot on the jet? If so, I'm pretty sure that was caused by me as it is a bit awkward to get a screwdriver to it without taking other bits off and I used a smaller driver than I perhaps should have.

When I started investigating the rich running, that was probably the first place I started (should have been the air filter... lesson learnt) and immediately noticed it was different from my Scotty..... hence the initial question "should I be able to adjust the mixture" the answer to which, I think, is now probably no.

The previous owned died some years ago and the mower was stored in a very nice garage up in he mountains. It hadn't been started in about 5/6 years before I got it. I am guessing that no one was ever in the carby, it was all fairly dirty and I've cleaned everything up.

Thanks for sticking with this I do appreciate your help. I also noticed another thread with an engine made the day before mine... I will put some pictures on it

Once again, many thanks for your help

Alistair

Thanks for the clarifications, Alistair. It seems, then, that the rich mixture problem is not due to foul play, but is a genuine malfunction. Does the smoke happen at all speeds, and is it continuous if you run the mower at full speed under a fair amount of load, e.g. if you hold it back as it mows? And is it always black, with the characteristic smell of half-burned petrol (like when you leave the choke on)? If it does, I can't think of any way for excess fuel to get through the carburetor except through the main jet. The fuel pump on the side of the carburetor just pumps fuel steadily into a small well in the top of the fuel tank. The well overflows continuously back into the tank. Thus, no fuel pump malfunction I can think of could cause this problem. (This is quite different from the situation with the older vertical crankshaft carburetors, by the way.)

Let's see if bigted or one of the members can come up with an alternative explanation. If not, it may be necessary to remove the carburetor and inspect its main jet, in case it has fallen out or has some similar problem.

Hi Grumpy,

Sorry for getting back to you so slowly we had a family function today and I just got home.

I do think things have changed since I changed the air filter. Before it was always blowing smoke, which was quit noticeable. Since I changed the filter it is less so and I an beginning to think that it may be OK. When I do notice the smoke now it is immediately when I open the throttle to full and the smoke is there for a second or so. I kinda think that that is OK but I would welcome any other thoughts.

Once again, thank you for your help.

Alistair

The carburetor has an acceleration enrichment function, Alistair, so if the throttle opens suddenly there should be a brief puff of petrol smoke. If you can remember the days when cars had carburetors, they did the same thing, for the same reason. If you advance the speed control smoothly rather than abruptly, it should not smoke, and there should not be any steady-state smoke regardless of the amount of load on the engine. If it is doing those things, all is correct and it will look as if there was no problem except for a clogged air filter element.

That all makes sense.... I also think the main issue eas the air filter.

I will keep an eye on it over the next few weeks, Thank you for your help and sharing your knowledge I have certainly picked up some good information

You're welcome adeas, that's what we are here for. I'll close this thread. If something else comes up, either send me a PM and I'll re-open it, or start a new thread - whichever seems appropriate.