A few mechanical questions

[thumperjsa]

First, When I open the throttle in 1st gear, when it gets to about 6500 RPMs, it feels like the engine wants to quit for a quick moment and then takes off again like I hit a turbo. Is this what people call a "flat spot?"

Second, after running a while in town, as I idle up to a stop light, the RPMs want to stay at about 2k until I almost come to a complete stop. then it goes back to a normal idle of about 1.2k RPMs. I think that this is two high as well and I probably should adjust it a bit.

I also realized today that the clutch cable adjustment is all the way out at the clutch lever (screw all the way backed out). This does not seem right. I had the clutch rebuilt at a local shop that wrenches old and new bikes. Since then, that mechanic is not there. The clutch seems to work fine where it is at but I am worried that as there gets to be more play, I won't have any adjustment.

Please let me know your thoughts on these.

Thanx.

[TopCatGr58]

Hey there Thumper,

Well, it could be a flat spot, but I would think you would experience it in more than just 1st gear!? I'm assuming you're doing a slow roll on, vs. WOT?!?! It could be your timing plate, advance mechanism sticking, so you might want to pull the left timing plate cover off and check it for smooth operation, and that your vacuum advance pulls and holds, and then returns smoothly!?

Your idle is a bit high, usually around 1K is where most folks have it! Check your throttle cable and linkage to make sure it's not catching on the rubber boots and clamps that mount the carbs! Your carbs may also need to be synched better? Sounds like you have had it worked on at a SHOP vs. doing it yourself, so you can't be sure what or how it was done!?

Your clutch cable and actuator has an adjustment under the right side cover, and so you can start there! After ensuring that it's adjusted right, then if you're still at the end of your handle adjustment, then your cable just may be stretched a bit, and it may just be a matter of getting a new one!?

Okay, just a few of my thoughts, hopefully others will chime in as well!

[Dennyz]

1) 6500 is a strange place for a "flat spot". I guess you could have one or more lazy sliders. That is to high a RPM for the ignition to have much to do with it. It could be your clutch slipping. Does it do it in second gear at a lower RPM?

What type of air filter(s) and exhaust system does you bike have. If you have custom components, it could be a jetting issue.

2) What you have discribed is typical of having the idle mixture set to lean and the idle speed set to high. If when you go to turn the idle speed down, the engine will not idle smoothly, try turning the idle mixture screws 1/4 turn counterclock wise.

3) As TopCatGr58 indicated, first check the clutch engament linkage under the clutch side cover.

That's my $0.02

[thumperjsa]

I don't usually wind it up in second gear. And when I have in the past, I don't recall it happening. I don't recall what speed I would be going in second gear at 6500, but in first, I am already near 50 I believe. Sometimes I can't believe how fast this bike is, even with bad compression. All my cylinders runs around 115. Every oil change I add Marvel mystery oil and that brings the compression up a bit.

I will pull off the covers by this weekend and check to see if the advance is sticking. when I rev it up in out of gear, I don't get the same condition, but there is no load on the engine then.

Denny, I will also try the adjustments on the carbs that you mention this weekend. I pull the plugs and check them every once in a while. I am not real good at color tuning yet. I was able to to diagnose a rich condition on one of the cylinders that turned out to be a mis adjusted float. on my 3rd cylinder it was near 30 mm and I adjusted back to specs of close to 25mm. It may be running a bit lean because I am getting a lot of bluing on the 3 and 4 cylinder headers. Then again it could be because the MAC headers are not a s thick as some others.

As to the intake, I am using a plain airbox with a generic filter. My ride is an 80 but I have 79 carbs on it. I know this because of the air hoses on it and it has the larger main jets in it. The Carbs were synced earlier this year by the shop but I am no longer using that one because I think the mechanic was more stupid then I was. The owner recently sold the shop to a younger guy after retiring who not only is part owner but main mechanic. I have let him do a few things on my bike for me and I am much more comfortable with him working on it. I may go there to have the carbs synced since I don't have the tool for it.

Oh, something else I forgot to mention that Denny may have hit upon. When at idle at a stop light, I notice something that feels like ignition missing but it is not bad enough to normally concern with. It just feels like that though at idle with no load.

[chevy45412001]

throtle cable

i'd get a new throttle cable for symptom one. or at least check it. remove both ends of cable from were they are connected and move the cable back and forth by hand.You will know right away if the cable is culprit. The other problems i'm not good enough to give advice sorry. But i know from XSpereance and TC's help that cable can get ya.

[skids]

If you are about out of adjustment on the cable length at the grip, it is probably time for a new cable. I had one break on me once...that was an experience getting the bike home!

If you have a newer air box and an older carb set, make sure that the air nipples at the air box are not filled with plastic. If they are, you will need to drill them through for proper venting.

Even compression is probably a very good sign!

I am with Denny on the "flat spot" at high rpms. It seems that a slide is sluggish. Check the diaphragms for holes. Check the slides for sticking.

Originally posted by thumperjsa
All my cylinders runs around 115. Every oil change I add Marvel mystery oil and that brings the compression up a bit.

(snip)As to the intake, I am using a plain airbox with a generic filter. My ride is an 80 but I have 79 carbs on it. I know this because of the air hoses on it and it has the larger main jets in it. (snip)

[Dennyz]

Carb sync'ing

You can buy the tool for what it would cost to pay somebody to do it one time. It is also a good diagnostic tool to have around.

Sync Tools

I use the $40 unit and it has worked great for years.

I may go there to have the carbs synced since I don't have the tool for it.

[xssiveone]

Or, if you're like me and don't want to mess with mercury, you can buy a gang of 4 vacuum gauges like this one sold by JC Whitney Sync gauges

The mercury ones may be a bit more accurate, but for general street riding I don't think you'll ever notice a difference.

Either one will do. Adjust the carbs so each one is giving the same reading (doesn't matter what the reading is, just that they are all the same).

[chevy45412001]

sync

just remember to follow the procedure for syncing carbs,as one of them is the leader and the other three get adjusted to it.(iirc number three carb is not adjustable so you would sync the other carbs to #3's value).

[Ken Talbot]

Actually, you sync #1 to #2, then you sync #3 to #4, then you sync left side to right side.....

[John]

And the foot bone is connected to the ankle bone...

[mixelpix]

I am extremely happy with this carb synching tool

http://www.carbtune.com/
$93 + S&H from UK (3pounds, 5 bucks i think)

It has a convenient design - you can hang it off the handle while you work the throttle and adjust the screws, and it's not mercury! the rods are steel, which means a little more pressure is required for a minimum reading (8cmHg if i recall correctly), but you can basically turn it upside-down and use it for lower readings. Comes with simple instructions. 'course I also really like the colortune plugs just 'cause they're so darn neat!

otherwise:
JC $50 + S&H US
DK $75 + S&H US

-Patrick Kennedy

[gaffer77]

hi who is right??? chevvy or ken from reading a manual months ago i vaguely remember it saying exactly what chevvy says,but ken sounds about right to me in theory if you know what i mean but how do you adjust 3 when its got no adjustment??????????????????

[Czekus21]

The meathod that Ken quoted is What the book says. I've adjusted/sunk up carbs by doing 1 and 2. Then 3 and 4. then left and right. Came up with the same thing as just makeing them all the same. The vaccum gauges you can pick up fairily cheap. Whith all my carbs sunk up, the gauges read that there is an intake manifold leak. You can rule that out if you did your spray test around the manifolds with carb cleaner or starting fluid or wd-40. The vaccume gauges can be used on any vehicle with mutliple carbs. Including the early 70's model Fiat spyder. Having your carbs Sunk up means that they are all the same. In Syncro with each other. It is important to adjust them as close to perfect as you can get. There I said it... There's my 2 cents and here's another penny. Boy I hate scrolling the page from left to right. There. now I said that. Now I'll quite my crying and go make some food for my dog and I. Good luck

[Ken Talbot]

Sorry about having to edit out a bunch of your ???? marks, Gaffer - that's what was causing the wide display problem.....