CT70KO AT7B carb kit

S

Salukispeed

Member
I have a reasonably nice saphire blue 1970 CT70-KO and The carb weeps a tiny bit from the petcock and filter cap. Who has a QUALITY carb kit. with "proper" jets and float needle? Lots of Questionable parts on EBAY. A quick look at Dratv and I missed it if offered. Carb Number appears to be AT7B or possibly A17B. Runs ok but Looking at the spark plug it is rich and very dark with small areas of dark brown, Air bleed screw is nearly closed to get a reasonable idle which is odd as it is obviously already rich in some throttle opening ranges, Timing is spot on (F) both static and timing light. and valves are set to .002 in. C7HS plug and C6HS only slightly better Unsure where the Foat level is set right now.
 
If you’re unsure of float level - carb needs pulled to check . But you could pull carb cap and pull needle and at least check its setting . Be nice to the threads. Setting for needle is usually in the middle and leaner is moving it up or down means richer .
If your weeping you’re needing attention at some point but can still ride .There are plenty of spots to get good kits CHP
 
Thanks. It is third from top for the clip and just finger tight for the cap is good, Will mess with it more once I get a OE quality kit. and do the whole carb properly. Have a good day
 
I found and Ordered a factory Kit so in a few days I can tackle a real rebuild. I have had the bike for many years 35+ and resurrected it from a non running pile of ??? and have no clue who or what has been don to the carb in its first ten years. but i remember lots of scrapes and scratches. stripped screws. from PO attempts. I find many times the jets have been abused with wire and tip cleaners that ruin the hole. I have Metric and number drills that I could try to confirm the size but What is the correct size for a 65main and 35 pilot. if those numbers are correct. I just got back from a 5 mile ride with the needle clip now moved the top gruve and it is slighter better mid range 25-28 mph 1/2 throttle?? and now with a tiny bit of brown color from coal black plug, so I hope the float level is drastically wrong. Another indication is it runs better as it starts to run the bowl out with the petcock closed and starts with no or little choke on a cold start 80 deg day. I now have all my neighbors and friends laughing at the "OLD" guy cruising the neighborhood every chance i get. and the police have now politely told me to take it home two times!
Please chime in on thoughts besides my mental state!!
 
OE carb kit and new OE float needle and seat arrived yesterday. I noticed the old needle spring pin was worn 20% shorter, the spring was much softer, and tip was worn on an odd angle, probably changing the float function significantly. Old one was set to 20mm but could not really even hold the float weight effectively. and sagged if even a little beyond holding the carb body vertical. Hope the new parts cures the overly rich condition.
 
OK
Sorry for the long winded never ending post But totally at a loss now. Everything to spec at 20 mm and proper 65-35 jets 2nd and 3rd from top needle clip. and pilot screw adjusts more normally at1 1/4 ish. Runs very well and possibly slightly better performance noted on same hills and rout. with the new float parts. yet the plug refuses to lighten up . still pretty black. and even with a C6h plus. Any reasonable thoughts?? Going to go back to the basics like air-cleaner and cam timing verification. Does the AT7B carb use a oring on the emulsion tube. Has anyone else run a RC7HS plug this doubles the resistance in the secondary circut??? It runs fine and no issues so far but I went back to the standard. . This is what the local Napa was able to come up with. and the air filter is OE and no nests or rags in the housing. . I did oil the filter foam a little //
Thanks
 
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Try setting the exhaust valve clearance at .003"
Is the inlet "snorkel" on the air cleaner? These can easily get deformed, crushed and restrict air flow. Remove, retune and retest.
how many miles on the motor?
do you have a compression tester or a leak down tester?
 
Yes the snorkel is on the cleaner and undamaged or restricted that I can tell. The motor is an unknown miles, but has a new Dratv piston/rings and cylinder as of this summer. and seems good. A questionable part may be the new intake valve since the seat was very worn and has a 2mm wide sealing surface but does not seem to leak when gas was poured in the port when the head was off. I have a new head but i from a cheap chinese top end kit from later year. that would need the combustion chamber opened up to even try. With this comes the question?? since the new head has roller bearings and the original has plane bearings, how might this affect the oil supply to every where else if this removes any restriction . Some roller cam bearing motors use an orfice to limit flow? Thanks for your thoughts. as this is perplexing and difficult to get my mind around??
Valve sunk in too far and not enough spring pressure???? A thought?
Leak down test if I have a 10mm adaptor. Thoughts on % to expect?
 
You might want to buy a new cheap Chinese carb to try before you start swapping heads,, I’ve personally have had several original carbs that I replaced literally everything in that would never work right…I keep one Chinese unit around for just a test carb..
 
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