AM Carb Mods-Zama C3M

[Poleman]

Well, as some of you know I mod the aftermarket carbs or OEM, for the Hot Rod Dolmars and Older Husqvarna XP model's.
For the last half of year it seems like the carbs have changed in design. I've recieved the Zama C3M copys with no jets and have been discussing this issue with the distributer.
After dealing for the past several months with them and getting one good shipment outta four in I have a big stash of the carbs with no jets. I can't seem to get anything resolved from supplier so I sat down and really looked at one today. Needless to say I have a few to expiriment on.....so that's what I did.


These are the carbs I'm talking about.....no primary or auxiliary jets to drill or pull.
I ended up drilling the brass jet on the top to .052 from .037 stock. Reassembled and tested.....to my amazement the saw ran and tuned....other than the Hi. I was testing on an unlimited coil Dolmar and it wouldn't reach the rpm's I was wanting, and the H was closed.
I took the carb back apart and JB welded the hole at the end of the H screw. Well to my amazement.....again it ran and tuned this time the H also. Pretty good idle, good throttle responce!! Now I need to get it in some wood to see if it really helps or what we've got. Judging by piss review the saw and by the way it sound it may be a winner. If so using this carb would be way easier for modifications as no jets need to be pulled.
After getting in wood I will be experimenting on drill sizes and replicating the results to be sure they will be consistant.

I'll keep everyone posted on this....I'm sure there is some interest.

 

[mdavlee]

Cool Rich. Glad you figured out something to do with these carbs you had piled up

 

[psuiewalsh]

Interest.

 

[Poleman]

Lol....me too Mike!!! No spinning my wheels on then any more!!! Lol

 

[Poleman]

Well....update here.
Got to test these carbs today....it was a win/loose situation.

Started out with 9ne of the molded carbs already on the saw (#2). This saw started well but was kinda funky to start with until the saw warmed up, it then settled down and was ready to run. I set max rpm to 14-14,2. The saw really ran good and produced great torque in the cut.....you could really dog in with it!!
Tried carb 1 next (this is the one I figured would be best).....I couldn't get the saw started no matter what I tried.....went to Walbro. This will be covered in another post.
Put a molded Zama on to see if I could tell any difference. It ran good but I think I liked the #2 carb better..it produced more torque.
Tried the #1 carb again to no avail.
Thought I'd try the #2 carb again......now I couldn't get the saw started again with this carb. In the process off all the pulling ( almost 200lb of comp) on all this trying these carbs today I blew out the starter pawns so day over.

Overall I was disappointed in how things turned out.....I figured there would be issues changing carbs on a hot saw and I was right. The #2 carb was the best carb all day after dialed in. It restarted fine on first time run. Trying to decide if there were saw issues with the difficulty starting after warm.
I did find that the carbs (1&2) without jets needed a lot of L needle to run right. H was easy to adjust on these and you could set the high ram's where you wanted it.

I think these carbs have really good potential....just need more refinement.

 

[Poleman]

Well, got two of these carbs to function as far as starting, tunability and idle. The only issue I have is top rpm's......or according to my tach. The saw sounds faster than what's showing so to check that I may need a new tach.
I have the H totally close and only getting 12,8k.....other than that I like how the carb tunes and runs.
Next try will be with a smaller drill to see if the size I used is too much for the saw I'm using (6400 unlimited) my try on 7900+ to see what high end is.

 

[Poleman]

Ok, today's testing results. A little baseline on what it did and carb spec and how they performed.
Previously I tried two carbs, one I could not get to even run and the second day drilled to .052. This carb ran good other than top end...H closed and only 12,8 on an unlimited saw. Not optimal.

Next carb today was a drilling of .048. Hard to tune, closed H again and everything adjusted through the L needle. Finally got it tuned so it wouldn't stall. This carb was very temperamental and not good.

Third carb today was a drilling of .045....BINGO!!!! This carb tuned well, idled well and had great throttle responce. This was on an unlimited 6400, with a 24 inch bar,that was stock. The saw was fun to run with really good power and throttle responce. I tuned it to 14,1 and had plenty of adjustment left.

Phase II: Same carb on warmed up 7900 with unlimited coil and 24 inch bar. It ran as good on that saw also. It gave the top end I was looking for with good torque on the bottom. This carb also cold started well and hot start was excellent also.

Is this carb as good or better than a modded c3m? This carb is pretty close, will have to see if anymore can be rung out of it.

At least I've found a way to get the single jet AM carb to perform properly and in comparison to the Zamas c3m.