ZAMA CARB MOD-CLIFF NOTE VERSION

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Poleman

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Well finally.....

I know a few of you have been waiting for this and others just want to know/see how it's done.

First off this is for the Zama C3M on Dolmar 6400-7900 and will also work for on Husqvarna 365-372's old style.

2015-03-18 16.33.54.jpg .
Tools you'll need.
Micro Drill Bits ,Caliper to measure and make sure of drill size being used.
Pin vice to hold drill bit for drilling
Modified pliers to pull main jet
Hammer and punch to reinstall main jet

Also if eye sight is poor a set of magnifying glasses. And a small magnet.

I drill totally by hand so I can feel what the bit is doing and when it goes threw the jet. I do this because there is a membrain beneath the main and auxilery jet. I can see no adverse results or efrecommendyou drill threw it.


2015-02-16_21.04.35.jpg
Here is the carb lay out, with jets identified.
I drill the main jet first then move to the auxilery jet.
I then use the modified pliers to get ahold of the main jet (firmly but not crushing). I find it will come right out when using a rocking motion. Again firm grip so it doesnt slip. You will probably deform the jet slightly wher you grab. Its just cosmetic. You can sand it smooth again but reinstalling it with a sharp rap will usually make the edges lay back down.

Next the mixing chamber hole under the main jet is drilled to .55 mm. This is the one constant jet size on all carbs. This helps ideling caricturistics.

2015-02-16_21.09.35.jpg
Drill the hole closest to the edge. Again very easy to drill by hand. Be patient.
The jets drill slghtly harder since they are brass.

Now look at the underside of the main jet you removed...is the membrain still in place? If it is you can reinstall the main jet...if not take your small drill bit and work it back in. The membrain can come out and block the mixing holes and cause tuning problems. I have not seen this happen with a true Zama only Aftermarket carbs.
This is why I drill both jets first so when I remove jet I can check it.
Reinstall jet with the hammer and flat punch.

At this point reassemble and set carb and install in saw for your first test run.

On a stock saw I would reccomend
.3 for main jet
.35 for auxillary
.55 for mixing chamber-this will always be the same.

Start saw and tune. If there are problems having enough idle screw to get saw to idle but saw is running good otherwise remove carb from saw as a hole will be needed in the throttle plate to give the saw more air it is requiering from the introduction of more fuel it is recieving

2015-02-18_18.36.52.jpg
Drill it on the top of the throttle plate away from the jet on the bottom. With stock I would recommend 1mm hole to start. Reassemble and retest saw, see if there is enough screw to set a satisfactory idle with more screw to spare.

Run and enjoy!!!!

Now for the brave and builders......LETS GO BIGGER!!!
This will be for the ported and Big Bored saws.

Jet sizes:
Main .3 to .35
Auxilery .40
Mixing chamber .55

When you go with bigger main and auxillary it also affects the top end fuel. You may find that the H screw is totally closed and you need more rpm's as the saw isn't reaching the rpm it should.

2015-02-16_21.13.05.jpg
To regain the high speed adjustment you will need to JB weld the high speed jet closed. Clean carb with a shot of brake clean and let it dry. Mix a very small amount of JB weld and use a toothpick to place a small amount in the hole shown. The carb will need to dry over night at this point.

This should give you the high adjustability back an H screw will be totally adjustable.

The carb should be close to adjusting like stock when finished. If you find you went to far on the main or auxillary just JB weld them shut and redrill to the size that worked better.
Like wise on the throttle plate, if your getting to much air take the plate off carb, clean and solder shut and redrill smaller.

I have found you can correct things with JB weld if you go to big on any of yor drilling or if you just want to try bigger.

I hope this helps all interested and makes things easier to follow compared to the earlier thread.

Feel free if there are any questions.

Thank you, Terry Syd for your encouragement and your wisdom......this is you Buddy!!!!!
 
Brad,

I does seem like a lot but the extra torque it adds to the bottom end I think is worth it. It adds fuel from idle threw midrange and makes the saw REALLY pull.
It doesn't affect top end as the Dolmars are limited anyway....but it really helps from idle up.

A stock Dolmar compared to one that has been modded just seems to have no torque/bottom end in comparison.
 
Thanks Rich

I talked to two guys who have run a Dolmar who's carb you worked on and they said there is a difference. I can't wait to try it on my 7910.



What kind of gains do you find with the 365/372? I have one of each stock.
 
Hey Rich, great write up!!
I was about to read through the other thread again to find exactly what you have here. [emoji106]
Question. Are your recommended drill sizes the same for 6400 - 7900?
I just picked up a used 6400 and can't wait to do this!
 
I would start at .30-.35-55 for a stock saw for overall performance. If you put a 7900 top or a BB kit you can go bigger. Some of the choices is what you will be using the saw predominantly for, big wood or overall. If your into big wood most of the time 30-40 is good...lotta torque. At that setting if your Hi setting won't reach the 13,5k you can JB Weld the Hi office to get to that point. It should be around 12,8k with out.
 
Thanks Rich. I'll start with that. As far as rpm goes. I was checking last night and I couldn't get it above 13.2k and the limiter kicked in. I kept backing out and trying but that was as high as I could get it. Do you find it's better to just tune in the wood or use rpms on these saws?
 
No, pull the main jet and drill the bleed hole to .55 then put it back. That will help with any idle issues and makes it possible to go larger on the auxiliary jet if need be. You will only have to pull it once, all other mods are outside.
 
I'm bummed out...tried this mod but couldn't get the main jet out. I'm wondering if they started cementing them in place or something because I had a good hold of it, tried gently rocking, etc and nothing. Increased the pressure on my grip some more and ended up cutting the sides of the jet off. Nothing left to grab now...
 
Some are just hard to get out. Were you using a Zama Carb or AM? Some of the older Zamas are really tough and tight. I have seen some of the AM carbs with sealer but no oem's.....doesn't make a difference in getting them out.
What we're you using to pull the jet? I use a cheap set of nippers from a hardware store that I grind down. I can get right in at the bottom of the jet by the Carb, and makes very little marked upon removal.20140831_175430.jpg
 
Hi Rich, I'm guessing this is a factory original Zama since it was the carb that was on the saw when my friend bought it from Home Depot rental center. I followed the thread and made a pair of snippers just like the ones you have shown by grinding down the edge on my bench grinder. That dang plug wouldn't budge! I'll scour eBay for a new carb.
 

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