Mountfield SP474 with RM45 engine running lumpy (rich).

[Integrity]

Hi everyone, new to this forum and would just like to say hello!

I have a Mountfield SP474 with a GGP RM45 engine fitted to it. It runs really rich and lumpy. I have ultrasonically cleaned the carb twice, I have Fitted a new carburetter gasket kit, changed the coil and spark plug but to no avail.

I am now thinking that I have somehow got the gaskets mixed up causing my problem. I have searched on the Internet for a diagram showing the correct order and positioning of these gaskets but again to no avail.

Can some really kind person please advise me of the correct fitment of the gaskets or alternatively a possible solution to my problem.

Thanks in anticipation.

I remain yours very frustratedly

Integrity.

[Kapenta]

Where are you based? It just so happens that I have a brand new spare carburettor which should fit...

Does your carb bowl have two bolts underneath it, 1 of which is offset by 45 degrees?

[Integrity]

Hi Kapenta,

I am based in Derby and yes, it does have two bolts on the float bowl. Do you nick this may be my problem?

Integrity

[Kapenta]

Damn - I am Surrey based. The carbs are "disposables" - If you want mine, PM me and I'll send you photos this evening and we can come to an acceptable agreement?

[Kapenta]

Carb Cleaner is not good to use to start your engine, since it washes away any lubrication in the cylinder and can bypass the rings.

This is not good for aircooled engines, in particular, since they run hotter than equivalent liquid cooled engines and use the oil to carry heat away from the piston, as well as lubricate.

My tuppenyworth.

[mr_spock]

Does the float valve needle slide easily? I had some crud stuck in mine that only came out with some thin fuse wire shoved up it.

[Kapenta]

anonymous said:

[redacted]

I wasn't suggesting that you did, but a lot of people do! They just squirt it through the air intake...

[Integrity]

Hi again,

Firstly thank you for all the replies. It appears that all you people think it is a carb problem.

Right, I have removed the carb and yet again ultrasonically cleaned it. I then cleaned it again with carb cleaner. I subsequently refitted it and it ran perfectly for about 30 seconds, and then stopped ( it appeared like fuel starvation) albeit the fuel tank didn't appear empty I topped it up. It now starts up on choke and runs for about 5 seconds and then cuts out. It will restart immediately and again cut out after the five seconds. I am very confused.

I am now thinking of fitting an inline filter?? Any advice please?

Thanks in anticipation

Integrity

[Integrity]

Hi Kapenta,

Unfortunately I cannot pm you. Could you please pm me with the photos and your asking price.

Thanks

Integrity

[Evoluzione]

Kapenta said:

Carb Cleaner is not good to use to start your engine, since it washes away any lubrication in the cylinder and can bypass the rings.

This is not good for aircooled engines, in particular, since they run hotter than equivalent liquid cooled engines and use the oil to carry heat away from the piston, as well as lubricate.

My tuppenyworth.

We'll store that little gem in the folder along with 'Don't use Easystart as your engine gets addicted to it' shall we?

[Kapenta]

Evoluzione said:

We'll store that little gem in the folder along with 'Don't use Easystart as your engine gets addicted to it' shall we?

Fill your boots. They are yours to do with, as you please?

[Super Slo Mo]

What state is your air filter in? Giving this a good clean might help.

[Integrity]

Hi, thanks for your advice, at the moment I am attempting to run it without the entire air filter assembly being fitted. As above, it will start, run for a few seconds and then stop.

I am getting really, really frustrated with this issue.

Thanks

integrity

[netherfield]

I had the same problem as you describe,except it was an Honda engine,turned out to be the ignition coil that was faulty.

[Jonboy_t]

I had a problem almost identical a couple of months ago and there was a chap on here who had spent some time working on Briggs & Stratton engines who advised me to change the carb diaphragm and gasket as they can warp slightly and will cause this problem - you would never see this warping as it is so small, but it will screw it up! IIRC, it was about £3 for the part on eBay and took me all of 5 minutes (max!) to do. Problem solved!

ETA - just read your post again, seems like this may not be the problem!!

[mr_spock]

If you take out the float bowl bleed screw (the one under the carb at an angle) does fuel stream out? Keep a jar under it...

If not, either the float is binding somehow, or the float needle is sticking, or the fuel inlet is blocked. I cleaned mine multiple times with an air can and carb cleaner, and the only thing that removed the crap stuck in there was some fine fuse wire.

If fuel streams out, then you have a jet blocked probably, but I bet it doesn't. Or there's an air leak, my guess is at the carb to cylinder head mating surface.

[Kapenta]

Jonboy_t said:

I had a problem almost identical a couple of months ago and there was a chap on here who had spent some time working on Briggs & Stratton engines who advised me to change the carb diaphragm and gasket as they can warp slightly and will cause this problem - you would never see this warping as it is so small, but it will screw it up! IIRC, it was about £3 for the part on eBay and took me all of 5 minutes (max!) to do. Problem solved!

ETA - just read your post again, seems like this may not be the problem!!

I think that night have been me ?

[Tampon]

Kapenta said:

Jonboy_t said:

I had a problem almost identical a couple of months ago and there was a chap on here who had spent some time working on Briggs & Stratton engines who advised me to change the carb diaphragm and gasket as they can warp slightly and will cause this problem - you would never see this warping as it is so small, but it will screw it up! IIRC, it was about £3 for the part on eBay and took me all of 5 minutes (max!) to do. Problem solved!

ETA - just read your post again, seems like this may not be the problem!!

I think that night have been me ?

Oh you credit stealer !

I linked photos to aid identification, videos on how to do the work and links for buying the items.

I am going to sulk in the corner for 40 minutes and then watch the Grand Prix and forget all about it.

(Jesus I been hanging out with women too much this half term)