Re: '76 RD400c -- 2smoker "Ginger"
Sorry if I offended you Kop. I'm no expert, but love two strokes and have a well running RD400c which I have tuned through many variations successfully. Still I'm only an enthusiast passing info that has worked for me, so take it with a grain of salt.
I have ridden all three sets of pipes. I have two sets of DG pipes in the garage that I rode for years and I was quite pleased with. Would even be willing to pass them on to another RD enthusiast for cheap. I had a friend let me borrow his spec2 pipes for a few weeks because he always told me the DG's were holding me back and his bike was down. At the time I was on a stock ported motor with modded carbs and I didn't think it was worth the money to upgrade my chambers. Well putting them on and jetting two up on the main, dropping the clip down two notches and bumped my pilot to a 35 and it was like a whole new bike. I ordered new pipes the next day, went with the Moto Carrera pipes cause Doug gave me a good deal and I ride a lot of freeway, so didn't mind a higher RPM pipe. The power band is not as smooth as the Spec 2's but I love the hard kick of the power band and the cleanness of the hydro formed pipes. In my personal experience (I'm no expert, just going off the good old butt dyno) the DG pipes don't compare to the other two I have tried. I have heard the Jim Lomas pipes have an even sweeter power band for street, but I have no experience with them and they cost a pretty penny.
This is what Garry from Spec2 has to say about the the DG pipes:
SPEC II
"12457 Gladstone Ave Unit F
Sylmar, CA 91342
818-837-1313
Hello,
Pictures are at the end of this e-mail.
Thank you for considering us for your motorcycling needs.We ran my dyno for the first time in 4 years. On a customer's St II ported street RD350 with our RZ350 reed package and 30mm carbs, it made 56HP (rear wheel) with SPEC II F1 chambers!
The customer showed up with DG chambers. The DG chambers made only 47 hp on the same bike. Yes, it is impressive that a simple swap of chambers produced 20% more peak power. But, the F1 chambers produced 15% more power everywhere else. I have preached about how bad the DG chambers are for years. I have finally proved it. There are people out there that spend a lot of money on their engine then throw the HP away with the DG chambers. A ported engine with DG chambers makes the same HP as a stock RD with SPEC II chambers."
Now about the air screw. He mentioned he was chugging with the throttle off which is usually a sign of the bike leaning out on the pilot circuit. Since he is running a stock set up and a 25 pilot is stock, it might just need a simple adjustment on the air screw. I assumed the OP would know that in was clockwise(richer), but you are right i should have been more specific with my post. I'm pretty sure adjusting an airscrew richer half a turn is not going to blow his motor. If it helps the chugging then he can see if he is within proper range of the air screw. If less than 3/4th turns out then try a 27.5 pilot which many people use on stock RD's.
Stache I'm attaching a guide that might help you jet your bike.
