Topic: 400F Carb Sync Questions??

[LoopsAndLogic]

My Haynes manual says to have the cm Hg rating of the vacuum gauges between 16-24.

Is this a misprint? A friend of mine says, "I always set every bike I get in, to 6-10 for the Vacuum reading".

I was kinda shocked when I heard this

 Could he have meant a different measurement when he said this??

 I've set one of my other 400F's that is completely stock to 22 cm Hg, and all the plugs have there insulators still white after 55 miles when I did a plug chop.

The air screws are set a 1-1/2 turns out.

 Kinda of worried I might be running that one lean and now my Cafe 400 too!!

 

 

[Gordon]

The overall level of the mercury in the tubes is of no real concern.  All that matters is that they are all at, or very near, the same level as each other. 

[LoopsAndLogic]

I'm not using Mercury gauges. Just Vacuum gauges that were bought at my local hardware store.

 But could a higher reading on the all the carbs cause a lean mixture?

What would cause the plugs to still look white even though the bike is completely stock?

Many thanks

[wardmoto]

A higher reading is an indication of a higher pressure differential over the drop in the venturi pressure when compared to atmospheric pressure.  Making them all match is key.  If there are differences, it effects the way the bike idles (the 350F it is as if a plug wire is removed!) and the crispness of acceleration...kind of tangible kind of not.  I know from personal experience, when the carbs on my 350F are out of sync, it sounds as if the motor is going to shake itself to pieces...with that being said, while I know better and have a manometer, I bench sync them and get really lucky every time.  Your sync makes all the cylinders happy with respect to each other...while it may have a very slight effect on mixture with respect to one cylinder to another, it is of no concern to you.  Lean mixtures are a result of a fueling circuit(idle mid mains...and they all over lap) that cannot keep up with the air pump we call an engine.  An engine is indeed nothing but, and if you move more air you need to move more fuel...carb slides off 1/32 or 1/64 with respect to on another means nothing to lean looking insulators.  Any pinging? What is the advance on your ignition...stock?  Does the advancer work smoothly??  A good digital pic of a plug chop could help.  Do 3, let it idle, run it under load at 5k rpm and a WFO into 8/9k...you said it is stock..?  Listen to that engine...they will tell you when things are not correct....

[Gordon]

But could a higher reading on the all the carbs cause a lean mixture?

You're confusing two different things here.  The vacuum reading from the carbs won't tell you anything about the air/fuel mixture.  All that matters with respect to the carb synchronizing is that they are all at, or very near, the same level as each other. 

[LoopsAndLogic]

Nothing is stuck and the advancer is working properly.

 No pinging, and the advancer is pure stock.

 I feel that under 4-1/2k rpm the bike has really great pickup, but anything after 5k, I kinda feel it lags.

All carbs are sync'd and are dead even, which I can tell with my smooth idle.

I can definitely hear the difference with uneven carbs.

 The bike is stored currently but I will try to get a picture of the plugs first thing tomorrow.

 So, my last question.  Should I follow the books Higher cm Hg rating or my friend, the mechanic???

Thanks a ton

[Gordon]

So, my last question.  Should I follow the books Higher cm Hg rating or my friend, the mechanic???

Thanks a ton

I've been trying to tell you that the overall vacuum reading is not what matters.  All that is of concern is that they are all at the same level.  Once you have them balanced, the only way to raise or lower the vacuum level would be to open or close the throttle, which would also increase or decrease the idle speed. 

[mb3000gt]

forget about the vacuum, make sure that the ignition advance is actually advancing. then check you main jets, verfiy that they are stock and havent been altered.

[Bodi]

I'd like to know how you plan to change the port vacuum. I think the guys telling you the actual reading is meaningless and to consider the balance are right - because I can't figure out a way to adjust anything except the balance with a given idle RPM.

[kslrr]

It sounds like the manual and your friend are reffering to the 'range of the gauges' used so that a more accurate reading can be taken during card synchronizing.  The white plugs are caused by not enough fuel, like wardmoto says.  Wardmoto, do you think that he is refering to idle speed set by way of the vacuum? or at such-and-such a vacuum is where the idle mixture should then be set   Just fishing.

[LoopsAndLogic]

YES! That's what I was trying to say. Thank you kslrr!

I don't know what to base my sync on. The book or the mechanic friend.

 I do see it won't have any changes on my mixture...... But could the air mixture screws throw off my readings while in the process of syncing??

 Thanks again

[Gordon]

I don't know what to base my sync on. The book or the mechanic friend.

Neither.  You sych them to each other, and the reading on the guages makes absolutely no difference, as long as they are all the same. 

The idle mixture screws will only affect the synch if they are not all set the same. 

[kslrr]

YES! That's what I was trying to say. Thank you kslrr!

I don't know what to base my sync on. The book or the mechanic friend.

 I do see it won't have any changes on my mixture...... But could the air mixture screws throw off my readings while in the process of syncing??

 Thanks again

I have never thought that the gauge ranges would give me a better sync.  My gauges go from 30in vac (pure vacuum) to 0in vac and from 0psi to 9psi.  I just adjust the carbs until the needles are close to being the same.   As far as setting the idle speed by the vacuum, I have never heard of that (if that was what you were saying).

[TwoTired]

I have the Haynes manual.
It says the HG reading should be in the range of 16-24 HG and they should be adjusted to read within 3 HG of each other.

You set your to 22 HG?  You're good to go on the carb synch.

Is your mechanic friend using HG numbers or PSI numbers?

You're problem with acceleration can be identified by installing clean plugs and doing a plug chop while the bike is under load above 5K RPM.
Read the deposits, if dark, its too rich.  If light, its too lean.  Adjust slide needle accordingly.

[LoopsAndLogic]

Yep! All carbs set to 22 cm Hg.

He was going on PSI. That knuckle Head could have told me that in the beginning

 Sorry for all the trouble guys..... And yes, I've done plug chops with new plugs and it's not as rich as I would like it to be.

I would think 1 50mile run would get the insulator at least dark tan.....But it's still kinda white.

[flatblack]

I feel that under 4-1/2k rpm the bike has really great pickup, but anything after 5k, I kinda feel it lags.

All carbs are sync'd and are dead even, which I can tell with my smooth idle.

Interesting.  Mine doesn't get moving well until it's over 55-6000 rpm.  No "pipe" per se; it just keeps winding.

You've probably got at least one clogged main jet, or a float level imbalance.  BTDT...

fb

[tmht]

Interesting.  Mine doesn't get moving well until it's over 55-6000 rpm.  No "pipe" per se; it just keeps winding.

You've probably got at least one clogged main jet, or a float level imbalance.  BTDT...

fb

I agree, something doesn't sound right. I have ridden a total of 4 400s now 3 stock, 1 very much not. All of them don't really start pulling until 5-6K.

[wardmoto]

350 is very similar and pulling might be giving it a little too much credit!

[flatblack]

I wonder if the lack of power above 5K might not be an ignition problem...

Timing and points gaps all set correctly?  Got new spark plugs and good caps?

Just curious...

fb

[wardmoto]

Don't look too hard for the missing torque below 4-5k...you might not find it.  This is of course assuming all is well with the gas and spark.  If it falls on its face above 5k, run it there and do a plug chop...cant see how you wouldn't notice a clogged main at WFO at 5k+.  These small motors are essentially gutless unless you rev them...but at 5k it should be ready to wake up and run.  I am not doubting you, but did you take off the points plate and check the advancer?  Did you take it off (remember its orientation relative to the shaft from where it came)?  I have two 350F's.  I know they are different, but 50cc divided by four is not that different.  My stock one is a sewing machine with cam chain rattle and a stepless power band.  My cafe is ok at 1-4k with a hole at 4-6k that I created and then is a spirited ride from 6-10k.  Stupid question perhaps...how is the air filter???  Run her up with the choke off and then put it half way on or so and do the same...does it improve or get worse?  If the air filtration is stock, are all the parts there that Honda installed?  These bastards are that damn touchy...my stock 350F is a POS with that underseat snorkel removed....go figure, it was jetted to breath through a coffee stirrer.  Keep us posted...