Fresh start, fresh problems

[Striker1423]

I have my 1975 RD250 converted over to a 350 fresh bore with Jim Lomas street retro pipes and an Economy Cycle crossover tube (large fuel line style) and manifolds. As well I converted her to electronic ignition with a Vintage Smoke Dyna setup at 1.8 btdc  (1.81 left and like 1.79 right. As close as I could get).

The air filter that came out of the bike from stock was unbaffled and the jets were 120 mains on a 30 pilot. Stock needle and 0-8 needle jet.

I replaced the main jet with a 190 main to start , left 30 pilot in it. Then ran it around the block a few times. It seemed kinda all over the place. Initially started fine after rebuild, but seemed to not like idling the other day. Turned idle screws up half a turn and raised idle to about 1400. Still stalls on occasion. Tried setting air screw to 1 and 3/4 out from 1 and 1/4, still died when cold. Seems to idle fine when hot.

I know I made a lot of changes to the bike all at once so it's a rough start with tons of new info, but the main thing was it seemed to be running rough,  surging at slow speeds every now and then, not taking throttle well. Carbs were synced before taking off bike and a quick check with my finger inside carb bells showed they matched each other at full throttle when I put them back on.  Top end felt lax as well.

I have to pull plugs to see but I wonder if its lean? 190 seemed a good spot to start since it is 5 main sizes over stock.

This is cross posted in ac rd club. Suggestions so far have been larger 35 pilot and main jet, and plug the EC crossover. Also pressure test motor. Which I might be able to do but for now I'll check with propane or ether around motor.

[2 Stroke Jamoke]

I'm no expert but I think you are way lean, if you do the dave f mod you would be closer to 200 main. If your carbs are stock I think you might need to go bigger, Chuck rebuilt a 350 at the gap last year with pipes and filters and I think he was in the 300's on main. Someone on hear can chime in . I will also say I have the jl pipes (rd400) and they scavenge ALOT. You will most certainly need more main. Cheers -Ian

[Jspooner]

Sounds lean to me too but how did it run before, or is this the first time running it since the 350 conversion and the mods? Are your carbs clean? Have you had the needle jets out and are they clean? There are many things that can make it run like that.

[Striker1423]

Sounds lean to me too but how did it run before, or is this the first time running it since the 350 conversion and the mods? Are your carbs clean? Have you had the needle jets out and are they clean? There are many things that can make it run like that.

This was the first time running it after all the mods were performed. I did run it on the center stand on the points once the pipes were on just to hear it for the first time, but switched it over to electronic the next day.

I cleaned the carbs (chem-dip, rinse, air gun)  last summer and rode it. Ran the bike through with sta-bil, then ran the carbs dry before storing it. When I did the work, I looked over the carb quickly and the jets weren't clogged, so I swapped the main jets to the 190 and put them back in the bike. Since the carbs will be coming off again, I'll dunk them in the chem dip. As far as the air jet, I always blow the passages out after dipping the carbs, but they are un-modified and perhaps something came dislodged?

The multiple carb mods I'm reading about are a bit of voodoo to me, as I know I would botch that kinda job with my mickey mouse set of tools. So if they require it in terms of reliability, perhaps I can ship them off to someone.

The EC manifolds were a very tight fit inside the reed cages, so I put a thin coat of Permatex case-half sealer on both sides of the gasket and one side of the carb boot to ensure a seal. Doesn't mean it worked I guess lol, but I was in a hurry as usual to hear the thing run.

[SoCal250]

I cleaned the carbs (chem-dip, rinse, air gun)  last summer and rode it. Ran the bike through with sta-bil, then ran the carbs dry before storing it. When I did the work, I looked over the carb quickly and the jets weren't clogged, so I swapped the main jets to the 190 and put them back in the bike. Since the carbs will be coming off again, I'll dunk them in the chem dip. As far as the air jet, I always blow the passages out after dipping the carbs, but they are un-modified and perhaps something came dislodged?

To properly clean the carbs you must dissamble them and remove the jets, then clean them with parts cleaner (e.g. Chem-Dip), then rinse and blow out with air gun. Dunking alone does not do much. The pilot and needle jet are usually the things that clog up first. I used to use a toothbrush on mine with Chem-Dip before I got my ultrasonic cleaner. 

[Striker1423]

I cleaned the carbs (chem-dip, rinse, air gun)  last summer and rode it. Ran the bike through with sta-bil, then ran the carbs dry before storing it. When I did the work, I looked over the carb quickly and the jets weren't clogged, so I swapped the main jets to the 190 and put them back in the bike. Since the carbs will be coming off again, I'll dunk them in the chem dip. As far as the air jet, I always blow the passages out after dipping the carbs, but they are un-modified and perhaps something came dislodged?

To properly clean the carbs you must dissamble them and remove the jets, then clean them with parts cleaner (e.g. Chem-Dip), then rinse and blow out with air gun. Dunking alone does not do much. The pilot and needle jet are usually the things that clog up first. I used to use a toothbrush on mine with Chem-Dip before I got my ultrasonic cleaner. 

Oh im sorry I did disassemble them fully. Should have mentioned that.

[Seizer]

I would pressure test it also. I found a couple of little leaks at the crossover tube and at the base gasket when I put mine together. A little cheap insurance and peace of mind.

[Jspooner]

If I remember right you live fairly close to me. If you can get the bike to me sometime next month I'd be happy to work on it for you. I also sent you a text.

[SUPERTUNE]

To be clear in my mind...are you still on the stock airbox or did you use something different?
I always do the primary needle jet conversion if running a crossover manifold system.
I never use bleed needle jet unless using stock manifolds.
Chuck

[Striker1423]

To be clear in my mind...are you still on the stock airbox or did you use something different?
I always do the primary needle jet conversion if running a crossover manifold system.
I never use bleed needle jet unless using stock manifolds.
Chuck

This is a stock airbox with a UNI foam filter freshly cleaned and oiled. I dropped the main jets to 170's and the bike runs much better. It was suggested to me to try smaller jets and I was only convinced when I took the bike out on a 45F day and it ran much better than it did when it was 60F a week back. Denser air when its colder.

Now the primary needle jet conversion requires carb modifications correct? I would have used my stock boots if that was the case, but they are old and were giving me fits so I bought what I could find, and the crossover tube boots were the only reliable new ones I found at the time.

[m in sc]

yeah with a stock box WITH LID ON you will be in the 155-165 range if i remember correctly. with lid off gets you in the 180-195 range. (estimated) . you can always plug the crossover for initial setup if you wish, but not nec. .02

[Striker1423]

yeah with a stock box WITH LID ON you will be in the 155-165 range if i remember correctly. with lid off gets you in the 180-195 range. (estimated) . you can always plug the crossover for initial setup if you wish, but not nec. .02

That seems about right since I can only imagine how this will run on a 90 degree day this summer. I'm used to snowmobiles and when you put aftermarket pipes on them when its super cold, they really need extra fuel. I guess I was just over-zealous with the jets. Plus it probably didn't help that I blew my snowmobile up this winter on a 5 degree day in the Upper Peninsula. Must have been a bit paranoid.

[Striker1423]

OK, so I wound up with a 160 main jet and a 1/4 inch hole in the airbox lid. The thing rips but still feels a little flat in the mid-range. Before adding thew hole the bike was kinda all over the place. So, it's a lot more responsive now. I was having so much fun on the bike that I went for a long ride and even ran it down the freeway. Ballsy? Yes. Especially since I wasn't 100 percent sure of the jetting. But, that brings me to the theory of plug chops and what my best course of action would be to do one.

I don't live in an area where long stretches of road are safe to attempt high-speed plug chops. But, after farting around on the bike all day and running it home, this is what I found the left cylinder plug looked like. It was a brand new plug. The right looks very similar. My mechanic friend told me that it was high-speed glazing caused by too hot of a cylinder temp. I'd like others thoughts on this.

https://i.imgur.com/6Y3lp8v.jpg

[Barrie]

I would say slightly too lean and wind the oil off a tad, ( that's just a bit more than a Knat's cock)

[Striker1423]

Well, this is the seemingly last thing that's bugging me on this bike. Not sure what this noise is, but it was making it last year on just the 250 as well. When warm it's got this rattle from the clutch side that gets the loudest when good and hot. Sounds like a bag of marbles. I figure it could be the clutch is just worn out, but I don't quite know. Again for the sake of knowledge the crank is new, etc. Clutch doesn't slip and the noise isn't really heard when at speed. But that is probably just from the wind noise. 

https://www.youtube.com/watch?v=MhU0yL9ymYE