Hi all, I recently purchased and installed a Sachs/Dolmar 3.4 engine on my extra 300 airplane. The engine was new over 15 years ago and has not been ran since. Upon receiving the engine I discovered a crack in the spark plug wire and promptly removed it, replacing it with a new 14mm wire and a ground wire coming from the CH ignition box. The engine did not want to run "open" and idled fine with a 22x8 and 22x10 JZ props. The engine surged and seemed to be running too rich from the start regardles where the needle setting were on the carb. This engine came with a HDA 23b carb so I located a rebuild kit for it and installed the new components in the proper manner. Fuel draw seems to be great and idle is fine with a sluggish transition fallowed by a surging burbly top end. Max rpms I coule achieve was 5400 with the 22x8 prop. I contacted Brison since they are familiar and helpfull with all engines and they suggested the small hole coming into the carb may be blocked or possibly gaskets misplaced within the carb itself. After dismantling the carb and cleaning with carb cleaner, small wire and high air compressor presure I have still the same problem. The spark plug seems to be building up lots of carbon followed by fuel spitting out the carb at higher rpms. I tried to use my hand as volocity stack and it didnt seem to help. Starting with the needles set 2 turns out and slowly adjusting from there the engine will sag when too lean and "load" up when too rich but the same sputtering surge at top end. The engine starts on the first flip of the prop and maintains a steady idle. I have changed the plug 3 times and use the recomended 32:1 breakin with ashless lawnboy oil and even cut it down a little to see if that would help. Timing seems to be on and I have adjusted it 5 degrees either way but no sign of clearing up. Spark is good with a new 4.8 volt battery which it suggested in the paperwork and fuel is steady to the carb. If anyone has had a problem simulair to this I would appreciate it if you could give me a idea where else to look for the problem. I wanted to send the engine to Brison but they consider this a chopped engine and prefer not to work on it. The engine was manufactured by T. G. MFG in New Jersey for airplane use in the 70's-80's and the ignition is the older brown box Ch ignition. Thanks and have a great day.

If Brison is afraid to work on the engine send it here...No problems with"chopped" engines..IMHO the genuine Sachs crank in the 3.4 is better than theirs...
Try a different C&H box first....
I KNOW, the Brison crank is guaranteed for 5 years now...Good move, the A&M crank it was copied from was junk.

Thanks Rcign1....... seems like you are about the only one that has ever answered my questions. LOL , I did talk to a few guys at brison and have to admit they are really helpfull and friendly. They did inform me the sachs crank is a real bulletproof crank and the engine should be good for a minimium of 1000+ hours. Although they said there was no way possible it could be a 3.4 engine and it must be a 3.1 or a chopped 3.7 they did happen to find the numbers I gave them off of the case to be a 3.4. The carb they suggested to try which may take away my problems was a DSC 80 carb which they use on their larger bore engines. I did not want to invest $50 in a carb if it may be the ignition or possibly the engine itself. I assume you work on engines and would be willing to take on this project ? I did not want to invest $80 in the ignition if it may be the carb[:'(]. Thanks and have a great day.

Another thought is the oil mix. Although it won't solve all the problems, the 32-1 mix usually loads up plugs extremely fast, causing running problems. Try a 40-1 or higher mix synthetic.

I can't imagine Brison being "afraid" to work on the engine, but could see how they may be too busy to.

A 15 year old ignition may have a bad coil or plug wire that is breaking down at high speed. Try another CH ignition set up for TCSA.

Hi,
One quick thing you can do if you have another engine is barrow the carb off of it. It doesen't matter if it is much smaller, at least it will tell you if you have a bad carb or not. It will still run ok, just not as fast. Make sure that you dont have leaks and the pulse port is open into the case. The HDA 23 was used in the Sachs saws and is 13.49mm. Any good Walbro about this size will give good power for flight.

Dave

Taurus Engines does work on those engines as well. see their web site.
Get rid of the 32:1 go with at least a 50;1 Klotz or Stihl oil
check the timing to set it 28-30 BTDC, set the plug at .022-.025
FWIW I would get a newer updated C/H
There also could be a leak in the cylinder head gasket.

Thanks for the info guys, I think I will visit the lawn mower repair shop in the next town and see if I can borrow a walbro crb just to try. The manufacturer states to not use any synthetic oils but the way the plug looks after 5 minutes of running you could chip the black carbon off of it and around the plug base. Thanks again for the info.

Thaats from running 32;1 manufacturers do that to protect the warranty. clean off the carbon from the piston and the inside top of the cylinder as well.
www.taurus-engines.com

A chopped 3.7 ? Hmmmmm....I know it's a 3.4, I have one here myself...They're heavier than the 3.2 so they weren't used as much...
The Carb is an SDC80, the price went up last year to about $73 retail...
The carb that came with it will be fine if it's working right...
Oil mixture ? Don't get me started on that one, its been debated ad infinitum here for years...
I just ran a G26, putting in more and more oil..Finally got so rich it just quit. Must have been richer than 10-1...Up to that point there was NO difference in performance, maybe a little better with more than it was with less....
I also changed the plug gap from about .020 to about .045..Ran the same either way....[8D]

Ralph,

The statement about changing the plug gap was a good point. Smaller gaps foul easier and provide a cooler spark.

Hi Ralph,
Have you checked the effects of plug on interference? That big a gap may not work well with other ignition setups.

Dave

Thanks for the info guys, just a couple more questions. Would a 18x8 wood prop be too small to use on this 3.4 engine and also since the original CH ignition had a shielded plug wire(wrapped with caseing) and I replaced it with a automotive 14mm wire and ran a new ground wire. Would this have any effect on receiver interference or spark leakage anywhere? Thanks

Yes to both...At least a 20-10 or 22-8 prop...

Ralph, running a .020-.045 gap did not show any difference. Did you check for interferrence of radio gear. Why do major spark plug mfg's recommend the .025 setting's as does most small engine mfg?

Ok, I did find out from CH ignitions that I do need to sheild the plug wire with a braided sheilding.....will a sheild from the local Farm and Fleet work? The sheilding they offer is a metal caseing that looks simuliar to the ones on the engines nowadays and seems cheap enough. Thanks

Spark plug gaps?
The bigger the gap, the more voltage required to jump the gap and make a spark.
If it's a magneto engine (as most small industrial engines are), the voltage from the mag is weakest at low rpm. So, they close the plug gap down to get a reliable spark while starting.

When you change to an electronic ignition, the voltage doesn't change with rpm. The plug gap should be as large as practical and still get reliable spark across the plug in the cylinder (under compression and with an oily mixture over the full range of rpm). That recommendation for the gap should come from the manufacturer of the ignition system. If they put more turns in the secondary coil, it'll jump a bigger plug gap.

Diablo-rcu, so what you're saying is that with an electronic ignition the gap should be wider.Or as wide as practical. How would one know what is practical. Say running amsoil 100:1 and 87 oct. what would you look for to determine the proper gap. Using 4.8volt battery and a C H ignition.

I took the side electrode completely off a plug and tried it...Still ran, but missed...I think somewhere around .050 would be good....I don't check the gaps on my conversions any more, just use the TLAR method, nice and wide..If if misses close it down a little
A really hot ignition will fire a really wide gap..I have a 1998 Dodge Dakota 318..FIRST spark plug change was at 92,000 miles..The gaps had eroded to about .080..Still ran great..New plugs made no difference at all, same gas mileage..It now has 176,000..That's 84,000 on the second set, still runs fine...

Thanks RcIgn, I am sending for a new carb from brison for $47 and a new ignition from CH. Together it will be about $150 but I will at least get the engine running properly. I will deal with the RF interference from there. Thanks for all the help and have a great day.