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Starting cold engine, how many turns of the throttle

Gsjj

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Hello all.. What is the average turns of the throttle to get your bike started. I have an 83 CB 750 and it is starting ok once she gets some gas flowing. I don't want to flood it, but it seems like about 4 turns. Once I get passed that cold start learning curve, she starts right up the first time once warm. So, there are no issues now, just trial and error I guess.

Thanks for any input.
 
If the engine is correctly tuned you need none at all, just use the choke and what it is for. One learns to moderate the choke as needed rather than the number of throttle twists.

One has to remember that most bikes do not have an accelerator pump setup and working the throttle on those does literally nothing like on modern MPFI cars now.
 
Hmm. Well, even new when my father bought it he said he always had to give it a few twists to start it. (When the engine was cold) it never just started up on the choke alone. Maybe something has always been off?
 
Possibly, never seen one that wouldn't crank instantly even in sub freezing weather. No multiple twisting of the throttle needed other than the small amount to keep it running once lit.

The choke if closing all the way in winter is enough to kill it from being too rich once engine has run for maybe 30 seconds max and in summer in 10 seconds you better be backing off choke partly or you WILL foul plugs. You DO need to hold throttle slightly open to allow more vacuum to form behind the butterfly to overpull fuel because the choke is closed. No pumping it at all though.
 
Hey, does that one have the vacuum demand valve still on it on right side of carb bank? That may change that, the fuel does not flow until engine is running and lots of people complain about them creating hard starts. Usually removed but then you need to practice turning the petcock off every time you stop the bike. One should be doing that anyway, it's a learned bike skill.
 
Here are my carbs, After reserching your question, I do not have the AFV you mentioned, but there is a black inlet in the middle of carb 2 and 3, maybe there was one there and it was removed? Should anything be connected to the inlet?


20170322_175329.jpg20170322_175339.jpg
 
The black pipe gets a longer rubber hose to drop behind carbs, it's the vent.

Look at your last pic and the third carb (#2) to the right, the brass fitting sticking out of the right of the front of the carb, that was the AFV vacuum source, you plug it to not leak vacuum.

Dunno what you have mixture screws set at but the idle limiters need removing or otherwise disabled and set them at 2 or 2 1/2 turns, all the same, the bike will idle better and slightly richer to start easier. The book figure is intentionally lean for emissions. Limiter caps are loctited on and a soldering iron held to them often lets them come off, I prefer myself to remove the tab on fuel bowl they bump against.
 
I see it. Looks like it was soldered closed by either my dad or someone who may have helped him in the past. Being this is absent, the hard starting may make sense. The fuel mixture screws are at 2. Something just isn't right. It takes about 10 tries and 3-5 minutes to start when cold. I am in Florida, when I say cold, it just means the next day.

What exactly does the accelerator pump do? Would that affect the starting?
 
Actually, it being absent should make bike EASIER to start. Why people remove them.

The accelerator pump pumps in a slight amount of fuel every time you work the throttle. Most bikes don't have them. What your working the throttle does, it replaces the choke which you really haven't mentioned at all. Does it even work? If not closing 100% you WILL have cold start issues.

FYI, those aircuts I mentioned in the past can really mess things up if they are cracked to vacuum leak. They feed directly into idle circuits. If your hot idle is not dead even then suspect issues there. You if idling correctly should have a dead even putt, putt, putt, putt, putt idle. There should be no lop-sidedness or lope to it.
 
Thank you amc49 for all your input and suggestions. The choke is working as it should (as far as my knowledge extends) so there seems to be no problem with that. I believe I read in another post of yours to hold the throttle open a bit (do not twist). So today I turned the choke on and did just that, held it open a bit. It started up in 4 tries, that was the best start up yet.

To me, that is a win. Let's see how she does tomorrow, but hopefully that will continue to get better.

Now, I am not sure if that is a sign of a different problem, but I guess I will eventually find out!
 
Many think the chokes are closing 100% until they yank the airbox to find they're not, the linkages are easily messed up to not pull quite all the way closed. 100% shut is just to get it started and up and running, you quickly have to moderate it open after that or it floods the engine. The DOHC does not have the spring loaded flapper doors in the choke plates that moderate choke somewhat automatically like earlier models did.

FYI, as a result test once when I was considering dropping the choke entirely in a high-perf carb set I tried for a bit using just the accelerator pumps to crank the engine as if there were no chokes on it. I found that here in Texas I needed 10-12 throttle pulls to even think about getting the same quick start before like with the chokes. And the added trouble of having to constantly gas the engine when it ran out of fuel while still cold. What a pain in the ---. The chokes work SO much better and I'm now pretty sure the way they extend to almost butt the slides makes them enhance the CV action as well to open the slides a bit faster.

Luck..............
 
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