Massey 135 question about perkins gas.

I posted a thread almost a year ago about a 135 perkins gas hardly running even after a massey dealer billed me $800 to repair. As a quick back story the points welded togeather. I replaced points , condenser, plugs, cap and rotor, rebuilt carb and could not get it running properly. Massey dealer replaced all the above, and tore carb apart again, also installed a coil requiring a ballist resistor and ballist resistor. It ran good for a few days then went back to the way it was before (hardly run, back firing only run with choke on) I was very frustrated so I left it in drive shed until a month ago. I disassembled carb again and checked float height. I got it running and have been setting timing.

After engine is warmed up my idle is 850rpm and timing set to 12 degrees BTDC. It idles fairly smooth but if I give it throttle to fast it will back fire a few times then clear up. If I hold throttle around 1800rpm it will back fire lightly once every few seconds.
If I slowly give it throttle it will increase rpms with no popping.
If I advance the timing to 30deg it runs slightly rougher but will accept throttlequicker. I also checked my advance by setting timing to 12 deg at idle then increase rpm to 2000rpms and rechecked timing and noticed its about 26deg which is per spec.

I think I am very close to having engine fine tuned just wondering if anyone has any suggestions as to why the engine will backfire when throttle is pulled to quickly?
 
Just a thought, something else to check- maybe valves clearance set to tight. What kind of fuel flow are you getting from the tank? Is fuel clean,
fresh, NO water?
 
While the tractor is running roughly, spray a little either around the intake manifold where it bolts to head and also around the throttle shaft where linkage hooks on. Lean mixture is why it backfires/pukes etc when accelerating. These are two areas no one ever looks at and usually the worn throttle shaft makes it backfire back through the intake and then blows one of the intake runner gaskets out. usually the center one on Perkins 4 cyl. You can't see if gasket is gone that's why the either. Give a try and let us know what ya find. Lean mixtures will mimic a lot of other problems.
 

Thanks for the reply the fuel is fresh and the flow is very steady. The valves is a good thought. To my knowledge they have not been set as long as my father has owned it. It is probly in need of a top set and was on my list of future things to do to it.
 

Randy thanks for the comment. What you described seems exactly what I am battling with. It will once in awhile backfire into the air filter as well as the exhaust. I will be checking the intake gaskets and throttle shaft and as mentioned by young mechanic a topo set is also over due.
 
I don't know about the carburetors for the Perkins gas, but on the carburetors for the Continental gas it has a 90 degree fitting that screws into the carburetor. The 90 degree fitting has a screen like a filter that gets choked up with junk (you have to take the fitting off the carburetor to clean it), like I said I don't know if the Perkins gas carburetor has that so it maybe worth a look.
 
If you go into the archives about this the last few years, you will find no good fix. I was told, and came to the conclusion, you must be patient with these Perkins gassers, because... they were designed to be diesels. That's as close an answer to your question as you can get for free.
They aren't designed for spark advance and up draft carbs. They will advance and suck fuel - differently than say- a Contental. I'd say it has to do mostly with the diesel's timing being slower than what most humans want to see out of a gas engine. So the advance of the throttle has to be careful, slow and don't expect great response. I find a spot where there is enough power but no stupidness, to get the job done. The less you move the throttle, the happier you you be.
My 2 Perkins petrols have gas pedals, so it is easy to get the coughing - so i let it catch up and try to remember to push slower next -attempt... of course, I could be wrong, and several thousands in work and parts 'might' cure this... but I doubt it...
 
i would be checking and setting the valves first thing, as they use a tight clearance and if not set regularly that maybe your problem. carburator or timing does not produce a backfire.
 
I don't care what anyone tries to tell you....lean mixture absolutely DOES cause backfire and usually back through the intake tract but will go both ways. I've seen it blow out intake manifold gaskets...then it gets even worse because more air leaks.
 

I appreciate all answers and not going to dispute. Everyones opinions is just that and worth trying. I drove it out of the garage on weekend and parked it and flooded it attempting to start it a few hours later. Pushed back into garage and tried it the next day and still nothing. Plan now is back to basics check spark and get going again. Set valves and check intake gaskets. I do believe these engines are very sensitive and requires patience. I will keep playing with it when I have time. Thanks
 
Well it has been awhile I took some time away from the tractor then started back at it. Here is the update. I discovered my #3 plug was not firing consistently. I set the valve lash, made a new intake manifold gasket ( unavailable unless purchased in complete kit) replaced exhaust manifold gaskets and down pipe gasket, new plugs, new cap and rotor, rechecked float height, rechecked ignition timing. Tractor starts like a champ and runs thru all rpm ranges with no popping or backfiring. As a added note I have decided to keep the tractor I'm memory of my father and will be installing a front end loader to it for snow removal and light yard work. Thank you for all the suggestions.
 

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