October 28, 2013 at 12:54 pm #14075
Long time lurker here, getting great info and help in learning about my DD2. I’ve finally hit the wall on my research and hoping I can get some guidance on a jetting issue.
2008 completely stock dd2, running 182 main, standard pilot and needle and 40:1 ratio. Living in So California, temperatures now a very mild 70-80 degrees. Issue is that I’ve got a lot of sputtering and blubbering up to about 7 or 8k, and then it takes off and revs out clean. If I have the choke on, no sputtering at all, and sounds if anything a bit too crisp. Figure that means I’m running lean, so lowered the float from 6mm to 3mm and the needle to 4th position. And realistically no change at all from these adjustments with a lot of white smoke pouring out. Plug is a bit of a dark brown. I’ve blown out the jets and carb numerous times and nothings appears to be clogged, with a clean stream of carby cleaner spraying in all sorts of directions typically.
Once it’s fully up to temp, it’s a bit better which also leads me to think it’s lean. But it runs great on top, so don’t want to mess much more with main unless that might impact lower revs? Also, new bellow on power valve operating very nice and smooth.
Everything in my jetting experience tells me it is lean, but then why would opening the choke clean it up? I’ve got many years of history with 2 smoke MX bikes and never ran into a lower rpm issue like this.
Any jetting tips or experiences on what I’m seeing here?
MarkOctober 28, 2013 at 5:29 pm #14101
Mark, I’d go up a full jet size instead of float arms and needle clip changes. If for no other reason to just see for sure if its too lean. That said, from what I’ve experienced an engine too lean will miss on the top end and pop. And since your’s is not, I can understand you trying the needle clip. Also regarding the choke, when you apply it you essentially richen the mixture across the board. Another reason to go up one main jet size.
When I had issues in the rev range you mentioned, it turned out to be battery related. So you might look there if the main jet doesn’t solve it.
Other Rotax check points: if the fuel pump diaphragm is old you might inspect/replace that and be sure all your fuel and vacuum hoses are tight and secured. Sometimes air can be pulled into the fuel lines. Or the pulse line can lessen the fuel pump’s capabilities.
Is your problem occurring all the time at that rev range? Or perhaps just when exiting a corner in that rev range?
Something suspect is the 7-8k rpm mark. That’s defiantly RAVE valve suspect range. I know you said you checked it, but don’t 100% rule it out as you step through other areas if jetting doesn’t work.
Lastly, as John Savage would advise: if you can swap carbs with a known good one, you can then begin to backwards trouble shoot. If you swap carbs and the problem still exists, I’d start looking at electrical.October 28, 2013 at 9:02 pm #14120
Thanks Eric,lots to think about. Regarding fuel pump I have the round plastic one, oem. Looking at mikuni pumps but not sure which model…44-210, 211 etc? Wouldn’t mind having that on hand.
For the battery, other than being charged, what else could be wrong?
And I will order another bellow for the power valve. Measures out to spec but can’t hurt to try another too.
A friend does have a spare carb, so that is probably the quickest test And eliminates many questions. Hope to get a track day and try that out.
At high Rpms the motor is strong and clean, so confident it’s nothing major. Having fun tearing into this and learning about the motor.
markOctober 29, 2013 at 7:17 am #14143
Battery-wise, as you probably know the Rotax is a total loss system. The battery is used for all running electrical. A bad battery can lead to misfiring and bogging. When I was new to Rotax, I used non-spec batteries as they were far less expensive, and I had all sorts of issues with the engine missing and bogging coming out of corners. Finally swapped to a YUSA Rotax-spec battery and the engines ran consistently well.
I had a fuel pump go bad once. At first the symptom was the kart was simply running poorly. As the issue progressed, the the kart would hardly run at all under load out on the track. After trying everything else, the light-bulb went off and I checked the diaphragm. It was fairly stretched from use. I had about two seasons on that diaphragm. Its such an easy thing to check and correct. I now have a separate rebuilt fuel-pump on stand-by just in case, and I visually inspect them regularly.
I’m not running DD2 (I’ve got a pair of Seniors), but the principles are the same. I do know the DD2 typically is jetted far richer than the non-DD2 Rotax engines. In the beginning, I was taking my kart to a near-by track that didn’t have many pro karts there. So I was basically all by myself. From reading the forums, you’d think Rotax was basically Voodoo when it comes to jetting and carb set-up – lots of threads about problems. And of course when you’re new to Rotax you’re not sure what is too rich or too lean. But I have to say once you spend some time with it, it really is a very robust package. These days I basically check the weather, run the data into a jetting program (like John Savage’s Jet Tech), install the specified jet and plug, and hit the track.October 30, 2013 at 7:04 am #14304
As Eric advises do not be afraid to change the main jet to see if that cures your problem you will not break your motor provided you are sensible
But as I always say try to borrow a known ‘good carb’ for a few laps and that will tell you if you have a carb problem or that you need to address other areas
Also have a good read of my jetting article which should give the basics of good practiceOctober 30, 2013 at 8:56 am #14317
I’ve read the jet-tech article maybe no less than 50 times, and it sits on my workbench. Thanks for such great info on both the jetting and PV setup. Definitely helped get me up to speed on what to look for.
when I bought the kart, it had a 190 main and was even worse, much worse and would barely run until I was screaming it. Yet keeping the choke on helped as it does now. Now that I’ve cleaned everything out no harm in trying to go up from the 182 a few sizes at a time and see if things go in the right direction.
Was supposed to have a track day today and was going to try a friends spare carb, but the track was closed for a private session…grrrr.
Ordered a new power valve, bellow, springs etc, Mikuni fuel pump and other bits to start replacing if the spare carb makes no difference. Though the kart is an ’08, it had barely an hour on it (per the mychron4) when I bought it last year. Prior owner wasn’t into it so it was essentially brand new. Everything is in perfect condition, fuel lines tight, Rotax oem battery, etc. Maybe I should just replace it with a nice new ’13 kart……
MarkOctober 31, 2013 at 7:46 am #14386
Mark, you say “Maybe I should just replace it with a nice new ’13 kart……” now that’s an expensive solution – LOL
I am sure that when you get to the track and complete your planned tests you will find a solutionOctober 31, 2013 at 8:17 am #14394
I bought my Rotax karts back in 2010 – a matching pair of 2005 CRG Kalifornia’s with same year engines. The karts had been sitting up in NJ for a year or so. I disassembled the karts and rebuilt them from the ground up. I then couldn’t even get the engine’s to fire up. LOL! So, I started sorting the engines. In the end, the 8-year old motors today fire-up nicely and perform smoothly on the track. And my karting experience is far better as a result of all the hands-on time fixing and fine-tuning everything. I was at the track yesterday and my biggest complaint was that I threw a chain. =)
Good luck!October 31, 2013 at 8:39 am #14395
The problem I have when I’m at the track is that I don’t want to tinker, just want to turn more laps. I don’t get out to the track often enough to be willing to spend the time and trouble-shoot, so I end up living with it . But I’m committed now as the kart is getting sorted out and this is the last issue…..actually once I get this figured out moving on to learning about the handling setup.
thanks for the words of wisdom,
MarkNovember 9, 2013 at 7:40 am #15139
On the underside of the engine you have a sensor for your crankshaft rotation.
Take it out, put an O ring spacer to have the sensor farther away from the crank.
I’m not running DD2 but a tuned Senoir, one day I was next to a professional team in the pitlane, running DD2 , they had the same problem. They changed carb, wirings,ignition coil etc etc. Madness. Until the moment a technician from another team came in and he told them to place the o ring spacer.
10 minutes later , problem solved.
I hope this will work for you ….November 9, 2013 at 3:06 pm #15155
On the underside of the engine you have a sensor for your crankshaft rotation.
Take it out, put an O ring spacer to have the sensor farther away from the crank. I’m not running DD2 but a tuned Senoir, one day I was next to a professional team in the pitlane, running DD2 , they had the same problem. They changed carb, wirings,ignition coil etc etc. Madness. Until the moment a technician from another team came in and he told them to place the o ring spacer.
10 minutes later , problem solved. I hope this will work for you ….
haven’t heard this one with my research, and will look into it. I did get the spare carbs from a friend and didn’t have a chance to try them. Got in some track time this week, and going leaner on the main helped, going richer hurt. Yet it still sounds better on choke. With the 178 the power was hitting maybe 8k and pulled strong, below that sounded like a loaded up old motorcycle.
Any idea what size o ring, or material?
MarkNovember 10, 2013 at 12:29 pm #15189
I will try to phone the guy next week and keep you informed.November 12, 2013 at 11:58 am #15388
He told me that the pick up has an original spacer, he has added the same one. ( 2 in total ). Hope this will work for you.November 12, 2013 at 12:06 pm #15389
He told me that the pick up has an original spacer, he has added the same one. ( 2 in total ). Hope this will work for you.
Certainly worth a try, and great info. I found one old thread somewhere that briefly mentioned the “sensor trick” but didn’t elaborate. Guessing I need to drain the oil to do this, and probably time for that anyways so will give this a shot.
Thanks for the help!
MGNovember 13, 2013 at 10:10 am #15488
The sensor 265560 is placed in the carter of the engine to mesure the crank revs , no oil there. Order part 431500.November 13, 2013 at 2:15 pm #15519
The sensor 265560 is placed in the carter of the engine to mesure the crank revs , no oil there. Order part 431500.
doink….I’ve been working on 4 strokes for too long….. No oil to worry about there. Thanks for the detail. Will include that gasket in my next order and cross my fingers.
MarkDecember 1, 2013 at 5:34 pm #16853
My friend lent me a spare carb he had rolling around his toolbox. Took it apart and it’s setup exactly the same as the one I’ve been working on. All jets, venturi, float height etc are the same. Bolted it on and fired right up. Ran on choke o.k. for a minute and then went rich, so had to turn it off. Exactly the opposite of how my carb behaves. Only warmed up on stand, so hard to say how it’ll run on the track, but sounds fierce compared to before. Revs faster and around 7-8k screams, which is how it should behave from what I’ve read. and once temp got up, smoking pretty minimal.
Have a track day this week and we’ll see if things are better, but appears to be something funky with my carb. I’ve cleaned it a million times, sprayed cleaner through every hole and confirmed clear as could be. Assuming the borrowed carb runs as well as I hope, suppose I could start swapping bits one at a time to try and isolate the problem, but hoping my buddy will just sell me the one that works right.
MarkDecember 7, 2013 at 4:40 pm #17375
Any updates?December 8, 2013 at 1:37 pm #17427
So I did get out on Wednesday, and the kart seemed to run better with the alternate carb. Fired up on choke but didn’t idle nearly as high as my old carb did on choke, or other dd2’s at the track. Idle screw turned all the way up. Engine cleared out much better once warmed up and the mid-throttle hesitation not nearly as noticeable. On track performance did seem slightly better with a more pronounced boost around 7-8k. But it was quite chilly which will make any engine run a bit stronger. With half the radiator covered, never saw water temp over 125 per mychron readings, so thinking it was not warm enough. Going out again this Wednesday hopefully and will tinker some more. After 20+ solid laps, plug slightly wet and black/brown running 175 main, 1000′ altitude about 55 degrees out. Flat out runs wasn’t cutting out so maybe need to still go a bit leaner?
Maybe that new Tillotson carb will be the answer 🙂
MarkDecember 8, 2013 at 1:55 pm #17430
Flat out runs wasn’t cutting out so maybe need to still go a bit leaner?
Never be afraid to experiment, one jet down will not kill your engine
Maybe that new Tillotson carb will be the answer
Now that may well kill your engine! Let someone else do the development and then and only when its fully sorted would you consider that option.
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