Archived Posts

[Admin]

If you switch to 3 into 3 chambers you can run the same jet size across all 3 carbs .

[Admin]

I've tried it both ways (so to speak)...

The standard jets for an L in CV carbs are 110 in the outside, 107.5 in the middle.
I then set my carbs as needles set on lowest slot (all the way up), pilots out 1 1/4 turns.
Bike idles and runs beautifully with no flat spots/hesitation and gets reasonable fuel economy.

However, if you use Keyster rebuild kits (as I did), you don't get a 107.5 main jet, so you have to use 110's in all.
When I had all 110's in, I found it made bugger-all difference to the way the bike ran in general use.
I think from memory (more than 12 months ago now) it changed the pick-up (not sure why) slightly to being a tiny bit more responsive, but I think it surged a bit more on the over-run, which is strange because the main jets shouldn't have too much bearing on things until 1/2 to 3/4 throttle.

I reckon if you can get hold of a 107.5 or equivalent one-size-down from the rest of your mains, I'd use it. Suzuki had a pretty good idea what worked for these things.


Cheers
Paul

[Admin]

Over the years i have heard plenty of theorys about the center jet being smaller but the best one i have heard is the center exhaust being split into 2 pipes and with that design the return pulse might be better returning more of the exhausted fuel to the cylinder that the outside 2 ??

[Admin]

I guess what I will do is just keep the stock jets and read the plugs carefully, this GT hasnt been run in a few years hut i did here from the 1st PO that it ran very good the 2nd PO that I got it from just ragged it then let it sit. I found that the main jet needles where are set to full rich so I reset them to the stock setting . I just have to keep my eyes on it before logging any miles .

Whats a good burn in time on the plugs? how much time do I need ( non riding ) to get a basic read on them?

[Admin]

To do a proper plug chop you need to run the bike under load for at least 1/4 mile wide open and then chop the throttle and check the plugs.

Unless the bike is warmed up and operating under full load, the reading is not worth a pinch of goat s..t

The tip needs to be up to temperature and under full load that tip temperature rises enormously versus toddling along at part throttle.

Anything less that that is misleading.

[Admin]

i know stock spark on my beloved sohc cb750 is around 14k volts - which jumps to 40k volts (+) with a set of dyna coils

would like to know what coils are available for the T500, to bump up my spark voltage and eliminate 30 yr old ignition coils that could put me on the side of the road - just from being so danged old!!!
DFB

Dyna recommends their model DC10-1 for points systems. It's a 5-ohm coil with single secondary output and comes 2 to the package. But don't be fooled by what you read. Those 40,000 volts won't be produced unless conditions dictate. If you put your CB750 with the dyna coils on an ignition scope, you'll see around 12K to 14K volts at idle, depending on compression, plug gap, and firing polarity. Snap the throttle, and you'll see it jump to around 25k to 28K. The 40K might be developed at WOT and max engine load.

Your stock coils might be old, but they'll do quite well providing the plug wire and cap are in good condition and the coil ohms out okay. They can be repaired in a lot of cases. Primary resistance should be 4.5 to 5 ohms, and resistance between either primary lead and the end of the plug wire (without cap) should be 11k to 12K ohms.

Stu

[Admin]

for the little bit of time and money it takes to do, i like to ditch as much of the 40 yr old elctrical and ignition componants as i possibly can..

what your saying makes perfect sense, but i figure that while i am re-wiring everything, i might as well bump up the ignition as well...

plus, i like to relocate the coils from right on top of the motor and underneath the fuel tank, where it has to get hotter than a oven - and try to get the new coils mounted somewhere they are still out of sight , but where they get some air flow and ventilation..

good info there bud , i really appreciate you taking the time to teach me something that i wasnt aware of.. DFB

[Admin]

i lost the number for Jemco out of Houston, anybody have it?

umm, sad i know!


anyway - before i lost the number, i talked to a mr eaton down at jemco, and he mentioned they have 'street style ' pipes , any body have a pic or link to what they look like?

they quoted me 600 for swarbrisk and 400 for street style.. intrested to know all the differences,what that extra 200 bucks is doing for the bike


i love the swarbrick looks for sure - just wanted to know if there are any other pipes aroujnd, and if i might like the looks of jemco's "street pipes" even beetter thaan the swarbrick... plu 600 bones sees like an awful lot of cheese for me to cough up on pipes right at this particular moment..

thanks in advance guys, i know very little about the stuff thats out there for these bikes - i really appreciate you guys going through the troubel of pointing me in the right direction here.. thanks again , DFB

[Admin]

have alook in here as you might find what your looking for.


http://www.tiredironracing.com/pages/bikes2.html


http://www.jemcoexhaust.com/

[Admin]

If I recall right, the street style pipes do not tuck in like the Swarbrick clones. I think they allow you to keep either the side stand or center stand (or both) where the Swarbricks require you remove all the brackets underneath the bike.

Jim

[Admin]

Today I started the ole girl for the second time it ran much better than it did a few days ago, It seems to smoke a hair more on the left side . is that normal? the engine seems to run ok , I finaly got her to idle around 1100 rpm since I am still trying to remeber how to work on the old buffalo again thats a good start to me.

while running the engine I grabbed y point and shoot thermometer to see what it would do. I noticed that the exhaust temp was diffrent on all 3 cyls the RH was 135 cn was 210 LH was 175. I can figure that the right and left are a hair off because it's not completly sync'd yet but the center cyl seems a bit hot to be ? any ideas or am I just looking for trouble that aint there?

[Admin]

Could be.

On the last triple I rebuilt I used a digital pyrometer and had similar results.

I checked timing and then stripped the carbs and checked them and synched them again after making sure that all three slides opened together (one was lazy at first).

That improved things but still the center pot was hotter so I used CHT gauges with bimetallic sensors under each plug and ran them to a Mychron 2 to read the temps. All three turned out to be fairly close on mine.

Turned out that the center pipe and exhausts run at slightly different temperatures. The mufflers are also different but I seem to recall that the center pipe was hotter and so were the two small mufflers.

In the end I put it down to different back pressure in the center pipe.

Does anyone else have any experience to share?

[Admin]

Well I did little more tweaking and uning and caressing on the GT
I got damn near a perfect idle seems to respond to the throttle well.

still smokes more on the left side and if you crack the throttle from idle the right side card will backfire once as it is reving up .

any Ideas whay could cause these issues?

[Admin]

I just received a set of Jemco Swarbrick replicas last week for the TR500 replica road racer I'm building. The price is a high, but many a number of the guys on this board racing the 500's are using them with success so I thought I would go with experience on thios one. By the way, Jemco is running about 4 weeks beyond what he quotes in terms of turn around for these pipes...at least at this time. He is way backed up with orders....maybe another reason to go with him. If he had no backlog, you might wonder why???

[Admin]

If this bike has been sitting for a while, the smoking may clear up after all the residual oil is burned away.
I don't know about the backfiring problem, maybe an intake valve is sticking.