chrisjw Posted July 30, 2015 Share Posted July 30, 2015 I have 2 Force engines, one .21 & the other .25. I have the .21 tuned to perfection, but the other one is proving an absolute nightmare. It's either too rich or too lean. I just cannot get it running correctly. I've fitted new clutch shoes & springs, a new flywheel, new carb needles & a new exhaust.....& it has good compression.........There's no leaks anywhere & the heatsink is tight on..............It just seems to be one of those engines that refuses to tune properly...........I shall keep persevering, because I refuse to be beaten, but it is starting to do my head in..................... Quote Link to comment Share on other sites More sharing options...
HYPER-BOY Posted July 30, 2015 Share Posted July 30, 2015 Keep going! But, best method is back to factory tune, tune the HSN first then the LSN, then tune the idle. That's how I did it anyway and never had any issues, some engines took longer than others to sort. 1 Quote Link to comment Share on other sites More sharing options...
Nitroholic Posted July 30, 2015 Share Posted July 30, 2015 Air leaks are the usual issue with a motor that won't hold tune. With Force units, it's most likely the backplate o-ring. Also worth sealing the carb neck as well. I am assuming you have run both motors in the same car to rule out the fuel tank or air leaks on the fuel lines? The 25 I had was massively tolerant of a tune and ran well even when really rich and not tuned at all. Got to be some issue with this one, and you have covered most of them.. Only other thing I can think of is the front bearing has a failed seal on it. 2 Quote Link to comment Share on other sites More sharing options...
chrisjw Posted July 30, 2015 Author Share Posted July 30, 2015 Air leaks are the usual issue with a motor that won't hold tune. With Force units, it's most likely the backplate o-ring. Also worth sealing the carb neck as well. I am assuming you have run both motors in the same car to rule out the fuel tank or air leaks on the fuel lines? The 25 I had was massively tolerant of a tune and ran well even when really rich and not tuned at all. Got to be some issue with this one, and you have covered most of them.. Only other thing I can think of is the front bearing has a failed seal on it. Yeah, I used the same car on both engines, so have ruled out fuel lines etc.......When you say backplate, do you mean behind the pull start?.....I think I'll strip the engine down & have a good look..........I've started off with the HSN at 3 1/2 turns out from closed & the LSN flush............ Quote Link to comment Share on other sites More sharing options...
chrisjw Posted July 30, 2015 Author Share Posted July 30, 2015 (edited) Quick update.............I've just discovered a small split in the concertina rubber cover at the throttle end of the carb....This could well be the cause........Will need to try & source one from somewhere. *Edit...............I've googled the rubber boot & it doesn't act as a seal, just as a dust preventor, so it won't be that, although a new one is in order, as I've just split it further. Edited July 30, 2015 by chrisjw Quote Link to comment Share on other sites More sharing options...
Nitroholic Posted July 30, 2015 Share Posted July 30, 2015 Yep...the backplate is the bit behind the pullstart. It seals the back of the crankcase. When you take it off..be careful! Make sure the engine is clutch side down. In the end of the crank where the conrod joins there is a small hole. In this sits a pin and a tiny spring. This is what engages the pullstart via a little notch on the flat end of hte spindle which goes through the rear bearing. If you are not careful, the pin and spring can fall out into the engine.....which is bad if you don't notice.... or on the floor...which can also be bad as you have to go find the damn things! Manual link... http://www.ofna.com/pdf/eng-force25-26.pdf shows the layout. I found out the hard way....... Quote Link to comment Share on other sites More sharing options...
chrisjw Posted July 30, 2015 Author Share Posted July 30, 2015 Yep...the backplate is the bit behind the pullstart. It seals the back of the crankcase. When you take it off..be careful! Make sure the engine is clutch side down. In the end of the crank where the conrod joins there is a small hole. In this sits a pin and a tiny spring. This is what engages the pullstart via a little notch on the flat end of hte spindle which goes through the rear bearing. If you are not careful, the pin and spring can fall out into the engine.....which is bad if you don't notice.... or on the floor...which can also be bad as you have to go find the damn things! Manual link... http://www.ofna.com/pdf/eng-force25-26.pdf shows the layout. I found out the hard way....... I've had that apart just now & already learnt from the pin/spring saga from a previous strip down..............lol...........The seal seems fine, as do the 2 o-rings in the carb......One thing I have noticed when starting this engine, is that it revs really high on start up........more so than the other engine, which I presume could point to an air leak......I think I'll order a new silicone manifold gasket & spring too...........That will cancel out any problems with air leaks from there. Quote Link to comment Share on other sites More sharing options...
johnboy92 Posted July 30, 2015 Share Posted July 30, 2015 Bit basic I know but you changed the glow plug ? I know it can affect the tune happened to me before Quote Link to comment Share on other sites More sharing options...
chrisjw Posted July 30, 2015 Author Share Posted July 30, 2015 Bit basic I know but you changed the glow plug ? I know it can affect the tune happened to me before Yeah, tried that..............I have a new plug in there now, but thanks for the input............ Quote Link to comment Share on other sites More sharing options...
Nitroholic Posted July 30, 2015 Share Posted July 30, 2015 Don't need to replace the gasket...just get a tube of silicon type instant gasket. Best thing to seal carb neck and backplate 1 Quote Link to comment Share on other sites More sharing options...
chrisjw Posted July 30, 2015 Author Share Posted July 30, 2015 (edited) Don't need to replace the gasket...just get a tube of silicon type instant gasket. Best thing to seal carb neck and backplate Would I run the instant gasket jollop around the inside of the manifold itself & then fit the exhaust/manifold over the silicone gasket?..........& likewise, run a bead of instant gasket on the inside of the backplate? Edited July 30, 2015 by chrisjw Quote Link to comment Share on other sites More sharing options...
Nitroholic Posted July 30, 2015 Share Posted July 30, 2015 http://www.rcracer.com/2009/10/how-to-seal-a-nitro-engine-104/ 1 Quote Link to comment Share on other sites More sharing options...
chrisjw Posted July 31, 2015 Author Share Posted July 31, 2015 http://www.rcracer.com/2009/10/how-to-seal-a-nitro-engine-104/ Quote Link to comment Share on other sites More sharing options...
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