77 Jarota Timing/Valve Shim/Carb setup

angonemoto said:
All correct! Especially the first one. The other Bob is looking into the Mikuni solution. I like having a beta tester nearby.
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Still need to be set up correctly and not left sitting around for ages with fuel which will eventually go off and cause issues with them also. I see a lot of white residue crap on the floats in your photos, not to mention the internals look sad overall. Was never gunna idle with the slide wide open in your 4th photo.

All my Dellorto equipped bikes idle nicely thank you ! the big difference you will see with modern carbs is the throttle response and fuel metering which gives better economy and once set up they tend to stay in tune longer.  However no reason why a good set up set of Dell's wont hold much the same idle quality.

Out of interest what are your 4C cams set up at ?? asI dont see a degree wheel anywhere but you have the cam cover off, as this can have an affect on idle.  factory spec was at  102, 106 but I find that a lot of marks are not any where near that,  play around with these somewhat you can get better idle quality and also smooth out the power delivery somewhat  I use 101, 103 on he big bore Jota and the Silver bike is set to 101, 106 now and it hoots and idles great to boot  8) It was on the "marks" but way out on the clock.
 
Good call Brett, all the carb bodies and parts have been ultrasonically cleaned so were taking that out of the formula.
Here's more detail on the bike setup as I confess I may be missing something or just not as buttoned up on my process to solve the problem.
My dig on the Dellortos was sarcastic at best, as I'm fond of the tune I've found on my 2 750 twins with Dells under my ownership, these carbs are something altogether different and this is my first triple.

The timing is 32? BTDC at the crank with the cams set up at 104 inlet 113 exhaust at peak, lobe center, or max lift, however you prefer. The motor is Jota spec, has NOS Jota hi comp pistons, big bore collector and the 4C cams. B8ES plugs and DMC is set to curve 10 and I am considering that the #55 jets and super cruddy condition of the carb internals, bowls and floats are contributing to the poor idle. I have 58s and 60s on the way, along with rebuild kits and some random o rings and parts that I deemed were too questionable to use. This is set up with 135 mains, 265AB needle jests on K1s in the middle notch.

I should be able to report back this week or after the weekend on the results.

Its hard to say what will be the right combination in the end but at the moment the bike is too lean at 1.5 turns out.
 
Hi Bob as Brett suggested Cam timing can have a dramatic effect on low speed vaccumn and consequently idle.
May I suggest your maximum lift on your exhaust cam (if they are 4C cams) needs to be bought back closer to 100.
Every engine is slightly different but my 77 Jota that is a full spec Jota engine is happy with 58 pilots and cams timed at inlet 101 exhaust 103 the engine will idle at 800RPM quite happily.
Hope this may help.
 
I set my Jota's 4C cams at factory spec (lobe centre 102 inlet and 106 exhaust as Brett stated) and the bike starts easily, idles and runs nicely.

If yours is set at 104 and 113, then your inlet cam is retarded by 2? and your exhaust cam is advanced by 7? (the reason one is advanced and the other retarded is because the inlet figure is ATDC and the exhaust is BTDC)

Were your cams set up with that timing on purpose or is it just how they came from the factory? If it's the latter then I guess their quality control was a bit off when they drilled the bolt holes in the sprockets!

 
Every post is an education, and I really appreciate it.
The bike has had drilled cam wheels added, so it didn't come from the factory in this manner but were setup this way on purpose.
I just got the carb rebuild parts so fingers crossed I will get a good result or then, well you know. I have more work to do.
 
angonemoto said:
... were setup this way on purpose.
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Interesting. Was that something Scott Potter did? If so, I wonder why it was done that way.

With the inlet valve closing later than spec, you'll have reduced cylinder compression. The exhaust valve opening earlier will reduce the power stroke too.

I'd guess that these changes will reduce power in the lower end of the rev range. But at higher revs it may have less effect and could even improve top end power. Or will it? I dunno. The decreased valve overlap may impede scavenging at hither revs. I don't have any answers. I'm just guessing.

It would be interesting to see a dyno curve from your bike.
 
The 104/113 timing is as per Phil Todd's recommendation for the 4C, so I expect that the cam timing was intentionally set to these figures.   

Red uses 100/100 which works well for me.  I find that the 100/100 setting does have a slight tendency to induce pinking, but I perhaps this is because of poor fuel quality.  Our max octane is advertised as 95, but I suspect that it is less.  My Jota also likes 58 pilots.

Maurice's timing figures seem like a good compromise.

Tom
 
Hey all,
Yes, this motor was rebuilt by Scott and he set the timing up per Phil's spec, he drilled the wheels to allow for fine tuning in the future. The carbs weren't setup to this motor unfortunately so I'm sorting that out now. These were the carbs that were tuned to the stock Jarama back in 2015 on the DMC/2 and it seemed to run pretty well on my trip from NM to Tulsa.

All the new parts and jets arrived over the weekend so I will be able to get them back together this week, and will start with the 58s. Personally I would prefer lower end grunt over top end due to the spirited riding I do which is mostly about low and midrange acceleration on curvy rural backroads but for now I am going to stay the course with the timing. The motor ran rather smoothly in the garage we just had to turn out the mixture screws way out to get there. I really like the riding position with the dropped bars and rear sets. Reminds me of the setup I had on a KZ1000 that did really well on those rural roads. I'm excited to get this bike out there.

Our fuels here are really random, worse out in the Wisconsin outback and many stations have 10% ethanol as well. Octane ranges from 91-93 are available, but who knows what you are really getting. I'll also stick with the BE8S plugs for this first round. Like most of us I want to set it and forget it if I can. The bike will get ridden a lot and I hope that all begins soon.

I have access to a dyno so I will look into getting a few runs in on it this summer with the current timing.

Thanks again for all the support/comments. Keep 'em coming.
 
tom3c75 said:
I find that the 100/100 setting does have a slight tendency to induce pinking, but I perhaps this is because of poor fuel quality.
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100/100 will increase your effective compression stroke (not to be confused with CR) over the factory setting of 102/106 because the inlet valve closes a bit earlier. That could also be contributing to your pinking issue.
 
Thanks Cam, I thought that might be the case.  However, it does also pink a bit on 102 as well.    Worse on hot days, and varies depending where I source the fuel.  Much prefer the old leaded 98! 
I have pulled back the timing a few degrees, which helped a bit, but not completely. 
Tempted to try the 'bit of acetone' lark, but I'd hate to stuff up any non-metal parts.
 
i have CR stamped on the back of the maincases on my sfc 1000 , could it also be close ratio as in gearbox?
andy
 
Update in prequel to the weekend. All the carb rebuild parts are in, including the Cagiva sleeve kit. I'm on the fence on this. The Dell lipped edge manifold sleeves are now out of stock, so the work around is to trim 4MM off and mount the two pieces for the seal. Anyone else do this?
 
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