FZRSupport: the FZROnline Archive

There is a great photo of a home made carburetor sync tool in the WIKI section (everything you wanted to know about carbs) but I was wondering if anyone knows how critical the hole size of the MIG welder tip is? The wiki section recommends .045 for good air flow. I have .035 tips. Will these work ok or should I drill them out a little?
Also on the sync process, once carbs 1 & 2 are done, and then 3 & 4 are done...how do you sync 1&2 with 3&4? Do I have to fabricate a "2 into 1" hose coming off the intake boot for each pair of carbs? Tks

The cable is acting on carburetors 2 and 3. Simply attach your synch tool to 2 and 3 and adjust them. You are effectively adjusting 1&2 and 3&4 by doing this, since #1 doesn't move unless #2 moves, and #4 doesn't move unless #3 moves.

Don't think you will have a problem running the 035 tips. Just don't mix and match sizes. If anything the smaller tips might give you less bounce on the synch tool.

olie05 wrote: Don't think you will have a problem running the 035 tips. Just don't mix and match sizes.

great! thanks guys

vmaxmike wrote:Also on the sync process, once carbs 1 & 2 are done, and then 3 & 4 are done...how do you sync 1&2 with 3&4?

In theory - it doesn't matter that much. You can actually sync 1 & 2, then 1&3, then 1&4 which is what I did. I went back through all of them and they were spot on no matter the combination.

However; syncing combinations 1&2 and 3&4 first is the best solution. Then to finalize, you can sync 1&3 , 1&4, 2&3 or 2&4 - shouldn't matter as long as you are adjusting the screw between 2&3.

Since the screws are only able to independantly affect 1&2, 1/2&3/4, and 3&4 anyways (respectively from left to right), doesn't it make sense to just do the sync with those "pairs"? Then you can go back and double-check between "odd" pairs. Just remember that you can't adjust a carb on the left side to match a carb on the right side without adjusting both left side carbs (and vice versa). Or am I missing something here?

fzrbrandon wrote:Just remember that you can't adjust a carb on the left side to match a carb on the right side without adjusting both left side carbs (and vice versa).

You just have to know which sync screw to adjust. If you have already sync'd 1&2, then if you sync between 1&3, you would adjust the screw between 2&3. You could then sync 1&4 and adjust the screw between 3&4.

ragedigital wrote:

fzrbrandon wrote:Just remember that you can't adjust a carb on the left side to match a carb on the right side without adjusting both left side carbs (and vice versa).

You just have to know which sync screw to adjust. If you have already sync'd 1&2, then if you sync between 1&3, you would adjust the screw between 2&3. You could then sync 1&4 and adjust the screw between 3&4.

I THINK we're saying the same thing? LOL! As you already know, the screw between 2&3 effects 1&2 as a pair and 3&4 as a pair. The way to do it is to do 3&4 first (since #3 is the "master carb"), then 1&2. THEN, 1&2 are sync'ed as a pair to 3&4. If 1&2 are dialed and 3&4 are dialed, it's just a matter of balancing the two pairs (with the screw between 2&3). AT that point, I don't really see that it would be necessary to bounce between different pair combinations.

fzrbrandon wrote: As you already know, the screw between 2&3 effects 1&2 as a pair and 3&4 as a pair. The way to do it is to do 3&4 first (since #3 is the "master carb"), then 1&2. THEN, 1&2 are sync'ed as a pair to 3&4. If 1&2 are dialed and 3&4 are dialed, it's just a matter of balancing the two pairs (with the screw between 2&3). AT that point, I don't really see that it would be necessary to bounce between different pair combinations.

Brandon, I didn't realised that carb #3 was the master carb (where the throttle pull cable attaches to) I've checked, You are correct

I've always (Twice) adjusted #1 & #2 first

Thanks
Mal.

mawler wrote:

fzrbrandon wrote: As you already know, the screw between 2&3 effects 1&2 as a pair and 3&4 as a pair. The way to do it is to do 3&4 first (since #3 is the "master carb"), then 1&2. THEN, 1&2 are sync'ed as a pair to 3&4. If 1&2 are dialed and 3&4 are dialed, it's just a matter of balancing the two pairs (with the screw between 2&3). AT that point, I don't really see that it would be necessary to bounce between different pair combinations.

Brandon, I didn't realised that carb #3 was the master carb (where the throttle pull cable attaches to) I've checked, You are correct

I've always (Twice) adjusted #1 & #2 first

Thanks
Mal.

LOL! Glad I got one right!

lets not over complicate this simple process you adjust 1-2 then 3-4 then 2-3 while maintaining idle speed.

racerd14666 wrote:lets not over complicate this simple process you adjust 1-2 then 3-4 then 2-3 while maintaining idle speed.

From what Brandon says, synch 3-4 then 1-2 then 2-3. Viola

Mal.

racerd14666 wrote:lets not over complicate this simple process you adjust 1-2 then 3-4 then 2-3 while maintaining idle speed.

I don't think anyone here is trying to over-complicate it. My point in adding to this thread was actually to show that it ISN'T complicated (specifically that there's no need to compare a bunch of different carb pairs).

I don't want to over complicate things either, however I have heard things that you guys may want to take under consideration. My old man, someone who deals with physics for a living and has repaired countless amounts of older cars and bikes, rants on to me about how the "duel bottle" carb sync tool won't work properly and that the quad carb sync tool (measures all for carbs at once) is best method, only if there is a large fluid reservoir open to the normal atmospheric pressure.
Also a buddy of mine, he too has an extremely large amount of info on bikes (14 years of building, modding, and repairing just about everything on a bike), claims that the only way to really sync a set of carbs without spending larges amounts of cash on the dealership tools is by doing it the way he was taught in school; which is to find the master carb, open the idle up just enough to fit a long nail into the carb to slip passed the butter-fly valves, close the idle to where it just barely rubs the nail, and repeating the same method on all the other carbs. I asked him why a 2 bottle syncher wouldn't work, and he said that is because the idle jumps too much and the first carb will never be the same after you have made your way up to the forth carb. I know that you guys have had success stories with your carbs, which is why I am a skeptic about their statements. However, it makes me wonder if there is a possibility that one of them is right. Anyway, just thought you guys should know if you are on the quest for "the perfectly synched carbs".

Tell your dad to look up "differential pressure"; if there is negligible dP between carbs, they are synched. Quad carb tools are quicker and easier (less swapping of lines), but because they are measuring absolute (or perhaps gauge) pressure and not differential pressure there is a greater chance of error.

Your friend is talking about bench-synching, which is a legitimate way of doing it and can get you pretty close. Many of us do that on the bench (thus the name) after a carb clean-up, to reduce the time fiddling around on a running engine (ouch!). The problem is the differences in tract form can cause different flows for identical butterfly angles.

There is no RIGHT answer. Find what works for you, and stick with it. Your dad has his opinion of what's best for him; most of us here have our own thoughts.