Topic: 78 750F slow to warm up

[2wheels]

My 78F is really slow to warm up from a cold start.  Usually 5 to 15 C degrees in the morning here.
The bike has allways been like this and the choke does keep it running but it aint great till its ran for 5 to 10 minutes.  Then it is fine.
I think it is normal and is just the way the carbs are.
Is this true?

Can it be improved so it runs like my K0 750.  It just starts, runs great after about 30 seconds warm up.

[brewsky]

My 78k is the same....cold blooded when cold but great when warmed up.
Need to run with choke on first mile or so when cold.
In general, if a bike runs well with no choke when cold, it is richer than it needs to be when warmed up.

[Bankerdanny]

Later bikes are turned leaner so it doesn't surprise me that it would take a bit longer to warm up.

[HondaMan]

The F2/3 is the lean-burn setup. You can improve it by simply changing the primary jets to size #40 (use only Keihin's jets, though, can get them at JetsRus online) and if the mainjet is the #105 size, consider a #110, but not until after you have tried the #40 pilot jets first. You will find that the idle air screws will need to be adjusted inward about 1/4 turn when switching to the new idle jets.

[Paintedseat]

I'm using 38s and they are much better. Moved the needles to the 4th notch too. Only have to choke for 2 minutes before it will idle well.

[2wheels]

Great information.
I have to remove the carbs this spring.  They need new gaskets around the float bowls because they are seeping.  New float valves too.  But 40 years service is awesome.  This will be the first time the carbs are off this bike.

I was hoping to hear larger pilots would help.  So while apart i will try changing them.

[TwoTired]

Actually, if it is operated in cold weather routinely,  you can use a a Hotter spark plug, Like D7, to improve cold running operation and shorten warm up time.

Probably not good to use D7 in hot weather, though.  They won't take enough heat out of the chamber when the fins are all hot.

Cheers,

[2wheels]

Just to finish this topic.
I had to replace the gaskets on the fuel bowls because they were leaking.  The gasket set i bought had all the new jets ( not keihin).
I cleaned and installed all the original internal parts.
But i used the new slow jets.  Reassembled everything. The bike ran fine.  But had the same long warm up as expected.
I decided to experiment.  And drilled the slow jets out.  I ended up at 0.018 inches.
This fixed the long warm up.  The bike runs much better now

I now belong to the 100 club.  That is carbs on and off over 100 times.  It was lots of fun.
I know i could have just bought size 40 slow jets,  and would have ended in the same place.  Much quicker.