75 RD 350 is hard to start

[Overphil]

Recently went through all electrical components, rebuilt the carbs and tweaked my jets to 180 main and 25 pilot, needle on 3rd clip. Bike starts but stalls when you give it gas. I have to kick it 10 times before I can rev it up then it runs great. If I stop running it for a short time I have to choke it to start it. I tried going up to a 27.5 pilot but the bike would not start choke or no choke.
The bike has been hard to start since I’ve owned it and all the adjustments I’ve made. Any suggestions?

[tacky1]

Have you performed a compression test. Sounds like low compression. I’m rebuilding one of our dirt bikes that had the exact same symptoms.

[Overphil]

Yes, compression is good in both cylinders.

[MK]

I haven't experienced with such an old RD, but the LC & YPVS carbs have the choke jet in the left float bowl.
When disassembling the carbs the left/right side often gets swapped and in this case the choke system is dysfunctional.
The symptoms are exactly what you described.

[Overphil]

I researched the choke circuit and the float bowls are in correctly

[MK]

Then the symptoms still point to lean on idle and the bigger idle jet should have had a positive effect.
Are you sure the bike has the right carbs mounted? I'm asking because a wrong setup like too much slide cutaway could create similar effects.

What about seals and rubber? Everything ok and doesn't draw additional air? Test with stuff like brake cleaner or starting aid. Start the engine and spray on intake manifolds and cylinder intake region. If idle goes up with spray, you found a potential cause.

You could also do a leak down test, if you have the equipment.
At that age there's the possibility of the famous leaking crank seals - which leads to poor idle and also starting issues.

Other things would be ignition related.
Using Iridium spark plugs usually helps starting. Check for NGK B8HIX . If not easily available, the BR8HIX would do the job, too.

Check the ignition timing with a strobe light. Worn points can make it spark at the wrong time which can lead to bad starting.
Also check the running engine for sparks at the points.
If that's the case, replace the capacitor.

[Overphil]

Thanks Martin. I’ll try the spray check although I have carefully checked for air leaks around the boots.