Rotax 504E Popping Thru Carb Intake?

[comanche91]

More performance questions on the 95 MZ SilverStar Rotax 504E. The bike and Rotax are new to me, so maybe this is just how it is. Went for a long ride today (legally for the first time :thumbsup:), and noticed how RPM sensitive this thing is. If you don't keep the RPMs over 3K RPM, I get popping thru the carb intake, especially if it's lugging. After 3.5K to 6K RPM all is smooth, just runs like crap at around the 3K mark.

The bike had been sitting for a couple of years. I removed the tank, drained it all, put in fresh gas, a new plug, and new K&N air filter. I pulled the Bing 64 (32mm) carb off for a thorough cleaning. It looked very clean inside and I did not replace any parts, just made sure all everything was tight. I did not pull the top to inspect the diaphram as I do not have the correct tool for the screws, but I'm sure it's original. I'm suspecting the diaphram maybe? The bike has 8000 kilos on the odo.

It runs decently, and I may be worrying about nothing, but the popping in the carb inlet while lugging around 3K RPM can't be normal, is it? Many thanks for all the help so far guys.

[DAVID THOMPSON]

mine had a 18 tooth front sprocket and was geared way too tall 3000 up seem to be best on mine
in usa sprocket from rotax.net i put on a 17
and carb parts from
http://www.bingcarburetor.com/
for parts
and check that cv carb rubber diaphragm
dave

[comanche91]

mine had a 18 tooth front sprocket and was geared way too tall 3000 up seem to be best on mine
in usa sprocket from rotax.net i put on a 17dave

Interesting Dave. I've been thinking the gearing was way too tall all along. Looking in my manual, the SilverStar rear wheel ratio is 2.24 (17/38), the Tour 2.11 (18/38), and the Country is geared the lowest @ 2.38 (16/38). I have not figured out yet how to get to the front sprocket, and the SilverStar has that chain cover so even counting the rear sprocket teeth is a PITA. -Don

[DAVID THOMPSON]

plastic cover on right side also covers oil filter cover area
rear tire on my tour is 16 inch see what size is your tire
if 18 you may want a 16tooth and i think rear is limited by the chain sprockets
cover size
dave

[comanche91]

rear tire on my tour is 16 inch see what size is your tire
if 18 you may want a 16tooth and i think rear is limited by the chain sprockets cover size
dave

Yes, it's a 110/80-18" tire. 16 tooth it will be (after I verify the existing sprocket counts ), and it will give me a 2.38 final ratio, same as the Country. Will there be enough adjustment on the rear wheel axle to tighten the chain back to compersate for the smaller engine sprocket? Also, did you replace the chain when you changed the engine sprocket? Thanks Dave.

[DAVID THOMPSON]

i did nothing to chain other than adjust it there was room to change sprocket

a note about rear axle the nut on right side is adjusted and then it is tightened then axle
is tightened then your installed works different than any other bike i have worked on
axle screws into hub not the nut on right side nut on right is part of sprocket carrier

[Nozz]

I have the same experience, and I just avoid low rpms. It is happy above 4k, and sweet and happy between 4500 and 6000. Gearing is obviously a matter of taste. I'd personally never sacrifice the 75 to 85 mph end for a quicker take off, but that's just me...

I'm glad to see another enthusiastic mz/rotax devotee! It sounds like you have a good one with a lot of miles left to enjoy. I have 50,000km on mine and another in long term engine rehab. I have the stage one (two?) kit pending for that one, so I'll let you know if we ever get that back on the road with the cam and big dellorto.

Cheers,

Jim

[comanche91]

I have the same experience, and I just avoid low rpms. It is happy above 4k, and sweet and happy between 4500 and 6000. Gearing is obviously a matter of taste. I'd personally never sacrifice the 75 to 85 mph end for a quicker take off, but that's just me...

I'm glad to see another enthusiastic mz/rotax devotee! It sounds like you have a good one with a lot of miles left to enjoy. I have 50,000km on mine and another in long term engine rehab. I have the stage one (two?) kit pending for that one, so I'll let you know if we ever get that back on the road with the cam and big dellorto. Cheers, Jim

Jim, your bike may have been regeared by a previous owner? I do 90 MPH @ 4200 RPM now in 5th gear and there's room for more. Have you ever done a tooth count of the front and rear sprockets? That Stage I kit would be great. I called Tom Woods and they hadn't had any for the last ten years or so. Sure would like to get the pipe and muffler. The guy who used to make the pipes was long retired. -Don

[comanche91]

Well, it's gettin' there. Starts and idles great at 1200 RPM, but had a bogging down problem w. the Rotax under load until the revs went over 3K, then fine all the way up to redline. I got a Bing manual and the most probable cause for this condition is an obstruction or fault in the idle circuit. Made sense as tweaking the mixture screw had very little effect on the idle. I pulled out the mixture screw, and the 0-ring came out in pieces. Replaced it w. one I had (not a Bing part, but close), and it's much better now. So I figured it's time to order the basic rebuild kit for the carb from Bing (o-rings, diaphrams, gaskets) and go through it since I'm sure it's not been touched since new. I have not been into a Bing before, but assume it's basically like any other CV carb? Any pitfalls I should be aware of? And many thanks to the Dave-man for sharing his expertise to this MZ newbie.