yam 850cc triple, fixed carb jets!!

[TSNAPCRACKLEPOP]

i have a 1980 yamaha 850 triple. it has hitachis with fixed jets, pain in arse. any one know of how to change into screw jets?

[hardflex]

Don't know about the jets, but I have a 79 850 Special as my fun rider. It's been reliable as heck, but last fall I think I picked up something into an idle jet, as it doesn't idle as smoothly as it did. Still runs on all three above idle.

[TSNAPCRACKLEPOP]

my "77 750d was an abused bike with sidecar: carbs, petcocks and vacumm were a pain, found this one, much nicer. and this seat is very nice

[fastpat]

I'd see if there was a model of this carb with changeable jets on any bike. If not, then you have the decision to, 1. leave it alone (drilling the jet won't work), 2. extracting the pressed in jet, tapping the bore, and installing an adapter for a removable jet, or 3. doing a carb swap.

I had a similar 750 model, and those carbs were crap when they were new, the bike was never really smooth in around town driving.

Take a look at Keihin flat slide carbs.

[TSNAPCRACKLEPOP]

i do have a parts bike 1100 yamaha coming soon, i may use them, they are a small bit bigger

[David]

Clean what you can with spray carb cleaner. Remove the jets if you can. Strip some strand copper wire and use one strand to clean the jet holes.

Are they CV type carbs with the diaphragm on the slide? If so, check for tears in the diaphragms.

[tswaney]

Try this link and see if there's anything useful.

http://www.yamaha-triples.org/forums/thread-view.asp?tid=4379&mid=32904#M32904

I sold my '79 750 Special a couple of years ago, but still like to lurk on the yamaha-triples.org site; it is a really solid group.

My bike used the Mik II's so I can't answer your question about the Hitachis, but I bet someone there can.

[LakeCleElum]

Some of those jets are pressed in and can be removed with a pair of vice-grips. Be careful on the copper wire thing. The brass is very soft and it's easy to damage a jet.

Unless it's sat a lot of years in a hot climate, jets can usually be cleaned by carb cleaner and compressed air. The same applies to all passages in the carbs. Some models have metal plugs over the idle jets to prevent an owner from adjusting it. These can be drilled out. Then the jet can be unscrewed and the passage cleaned. One and half turns out is a good place to start upon reassembly.

Bikes from this era came set up very lean from the factory for emission reasons. Usually the pilot jets more so than the main jets. If you can't buy a larger pilot, you can find a drill bit that just barely goes thru it and then take the next largest one and drill it out. Another way to get it to run richer is putting a shim (washer) under the clip for the needle......G'luck..

[TSNAPCRACKLEPOP]

i have had the jets out, using small scrwedrivers and NEW long nose and hemostats, and cleaned the passages, and replaced the little "O" rings around the jets. i bet i mishaped the jets on removaql.

It ran UNBELIEVABLY well and SCARY fast for a day, then it returned to its stumbling ways. I am on the triples.org board too, so i guess i will order some of the remaining nos jets, or a size larger, and check those diaphrams when i disassemble them again. in KC, we have some nice winter riding days around Valentines Day, warms up the babes!

I am going to go get that xs1100 parts bike. He cannot start it even when he "jumps" it, but there is no solenoid on the motorcycle. (I sure miss old my xs1100 too!!)


and my "65 911, and 65 impala convert, and Devin, and 900/6 BMW, and 75/5, and 65 bug convert, and ......an nauseum.

"there"s always another "car" or "motorcycle"

are there substitute jet "threads" that i can insert, then screw the jets into? or machine shop cut the threads into the bodies?( a good friend could do this in this shop)\

thanks

tom

[hardflex]

Question... if you drill out the pilot jets slightly, you can still adjust the idle mixtures with the screws, right?

[fastpat]

Originally posted by hardflex
Question... if you drill out the pilot jets slightly, you can still adjust the idle mixtures with the screws, right?

Drilling out jets isn't something an amateur can do very well. First, it requires high precision to get the hole straight, and the angle of the jet is usually different for eash jet size. Jets are cheap, in most cases.

I rejetted my '86 FZ750's pilot jets up two sizes to eliminate an off idle stumble. The bike ran so much cooler, the electric cooling fan rarely came on after that. I think the four jets cost me something like $20-25.00.

[LakeCleElum]

Originally posted by hardflex
Question... if you drill out the pilot jets slightly, you can still adjust the idle mixtures with the screws, right?

Yes, IF there are adjustable idle jets hidden in there. In the early EPA days, some had a fixed idle jet that could not be adjusted. Your pilot jets basically control the mixture from idle up to about 1/4 throttle when the needle and slide take over. Main jet is for 3/4 to full throttle. There is some overlap of course....

[hardflex]

As I recall, I did have a bit of an off idle stumble. I haven't been into these carbs at all, but I'm going to need to, as I said I think a pilot jet is blocked. If I can't find new jets, just wondering at the option of drilling them. First, I'll study the symptoms more closely.

[fastpat]

Originally posted by hardflex
As I recall, I did have a bit of an off idle stumble. I haven't been into these carbs at all, but I'm going to need to, as I said I think a pilot jet is blocked. If I can't find new jets, just wondering at the option of drilling them. First, I'll study the symptoms more closely.

If the pilor jets are blocked, it's almost impossible to start the bike without priming it. I don't know about the carbs on your bike, but most pilot jets flow from closed to WOT, they did on my old FZ. The other circuits kicked in as the throttle was opened, but the pilot jet was always contributing to over all fuel flow.

[hardflex]

I think it's just one jet blocked, just hitting on 2 at idle but would kick in to 3 under power.

[LakeCleElum]

Originally posted by hardflex
I think it's just one jet blocked, just hitting on 2 at idle but would kick in to 3 under power.

Very common problem on bikes that have been sitting. Just pull them apart and blow out the idle passages, the pilot jet and the passage behind it. Don't make the mistake of just cleaning the jet and ignoring the passage the fuel flows thur....While in there, sit float levels, makes a big difference in how a bike runs....

[TSNAPCRACKLEPOP]

hardflex, the ignition wires on these bikes, the triples, often cause a miss. some have resistors in the caps, others do not. the high energy electronic iggy(the box can be opened and cleaned and dried out) after 1978 and moisture can cause a miss at low speed, as can the "primer circuit" (the vacumm tube above the intakes, or a cracked intake.

on mine, they are alum, but some are rubber, and crack with age(these bikes are now about 25 years old, time for wires)

also, on the left side, the connectors on the bottom catch the acid overflow of the battery bubbles, and both of the ones i had have had severe corrosion on the connections out the bottom of the terminals, heading over to the starter circuit. all replaced.

the jets are not adjustable, but the idle for the bike is adjustabler for idle on the linkage setup via a thumbscrew on early ones, and a screw on the newer ones.

i have talked with a guy here in kc who runs fast stretched 750 and 1000cc up bikes, and he also changes to larger jets, which is easy when they just screw in. look at my pix at the beginning of the thread....these are the jets, no cap over them, ....see the holes in them, those are the orfices. early triples, like the 750 2D, and Hardflexs' late 79 xs750 have the "anti tamper cap over the screw adjustable jet, but in 1980, they came up with a factory preset jet.

i heard a few bikes had this. trying to keep costs down, with a fix or other Yammy carbs is the plan, but if it isn't a dependable bike, i will not go around the block on it. m just wanted to touch base with the 2 wheeled crowd on this topic, and got some good info.

thanks to all, and pray for the sunny days!!!

tom

.