Jelmer C31 Posted October 6, 2016 Report Share Posted October 6, 2016 I have rebuilt my Mikuni 342, ultra sonic cleanded it and assambled it all again When I put the electric choke on again it holds the choke butterfly closed, is this normal? Does it pull it open when the engine is warm? Quote Link to comment
datzenmike Posted October 6, 2016 Report Share Posted October 6, 2016 Looks very much like an Hitachi carb. The choke had a bi-metallic spring inside. When warmed by the electric heater, the coil unwinds and pulls the choke open. Takes about 8 min and to some extent the outside temperature. When the choke cools the wire spring contracts and pushes against the choke plate. To set the choke fully, depress the throttle and it snaps closed ready for starting. 1 Quote Link to comment
Jelmer C31 Posted October 6, 2016 Author Report Share Posted October 6, 2016 Mike, it IS actualy a Hitachi ;-) ! Don't know why wrote Mikuni! Today I started the engine and it did what you said choke wise. So thats good. But the engine won't run below 1200-1300 rpm. The butterfly is open enough. Any ideas on this? Quote Link to comment
banzai510(hainz) Posted October 6, 2016 Report Share Posted October 6, 2016 In the United States for emissions the later carbs has a idle cut off seliniod so when you put key to off a plunger plugs the idle jet so the motor does not RUN ON after key is off. one wire will go to the choke and if you have a SELINOID you should have another wire or one is jumped(shorted from choke to the selinoid) that is you have this option. If you don't have a CUTOFF selinoid then you must adjust the mixture screw at the base of the carb . it will have a tension spring on the screw. you must adjust this and hopefull it will keep the car running at a lower RPM update going by your photo the selinoid in in the rear next to the bottle with the green labol. That looks like a Cutoff selinoid. so make sure that works and the mixture. Quote Link to comment
datzenmike Posted October 7, 2016 Report Share Posted October 7, 2016 I see your Idle cut solenoid top center under the green label. Has a red wire under a black sheath. Has to have 12 volts to it when ignition on. Turn ignition on, off, on, off, and if working, you should hear a clicking sound at rear of carb. Quote Link to comment
Jelmer C31 Posted October 7, 2016 Author Report Share Posted October 7, 2016 Thanks guys! I has indeed a solenoid bolted into the back of the carb. It also has another one on the side of the carb, you can see it in the picture in the left upper corner. Maybe I switced these wires. I also had th idle mixture screw out so maybe I need to back it out some more. In Europe these screws are "protected" by a metal case which prefents it from being adjusted so I will cut this of with my Dremel. and adjust it. How much do I back it out? My FSM says 2 full turns. Quote Link to comment
datzenmike Posted October 7, 2016 Report Share Posted October 7, 2016 The mixture is set at the factory and sealed. There is no 'set' amount only a general setting. It is set to what ever works for your engine. Make sure the solenoid is energized.This solenoid is a valve that allows fuel down to the idle mixture screw, and the slow speed circuit. Without fuel, it won't idle below about 1,200 RPMs. 1 Quote Link to comment
Jelmer C31 Posted October 7, 2016 Author Report Share Posted October 7, 2016 Thanks Mike. Ill dig into it tonight or tomorrow morning and let you guys know! Quote Link to comment
Jelmer C31 Posted October 8, 2016 Author Report Share Posted October 8, 2016 Got it running great again! First I checked if the solenoid was working and it did. Next was de idle mixture screw which I made a tool for so I could adjust it. I backed it out some and started the engine. It ran good on the choke but when warm it woudn't run again! I fidled aroud some and put my finger on a vacuum port which has to be hooked up at the airfilter: It ran great! It idled at 1200 but after I adjusted the idle adjsting screw at the throttle linkage it ran 850-900. Strarts and runs good now. I didn't test drive it yet but will do that this afternoon. 1 Quote Link to comment
datzenmike Posted October 8, 2016 Report Share Posted October 8, 2016 Idle and idle mixture setting... Warm engine, turn idle down. Turn idle mixture screw in or out. Idle quality may improve and the engine speed up or it may drop off towards stalling. Turn towards the best smooth fast idling You may find there is about one full turn of good idle with a drop off on either side. A sort of plateau. Set in the middle. By now the idle has gone up, so lower it again with the idle speed screw. Repeat the in and out adjustment, set in the middle of the smoothest fastest idle. Repeat as many tines as necessary, all the time seeking the fastest smoothest idle quality, until you can no longer improve it and the idle speed is 750-850. Turn adjustments slow enough that the engine can keep up. Engine idle should improve and become stronger. Always adjust towards improved idle quality. If idle is too high maybe 900 and above these adjustments may have no effect because you are up above the idle setting and in the slow speed circuit. In addition the mechanical and vacuum advance may be engaged making idle adjustments difficult. Quote Link to comment
Jelmer C31 Posted October 9, 2016 Author Report Share Posted October 9, 2016 Took it for a spin today and at warm up it does ok but when warm it stays at 1500rpm for a while when you let of the gas. If you press the clutch it stays there too for 5-6 seconds and than goes back to 800rpm. If you rev it in neutral it it gets back to 800rpm right away. So it only sticks at 1500rpm for 5-6 seconds when under load. Any ideas? Everything is working freely and is lubricated on the carb. Also all springs are attached and nothing sticks if you try it by hand. Quote Link to comment
datzenmike Posted October 9, 2016 Report Share Posted October 9, 2016 BCDD.set too sensitive. It responds to engine intake vacuum and holds the engine at a higher rev and slowly lets it down to idle. (it's an emission reducing device) If set too sensitive it sometimes doesn't release and drop to idle properly It's over by the top left behind the pistons. Pull the little rubber cover and adjust the screw inside by turning counter clockwise. This will make it less sensitive and allow idle sooner ot right away. Keep track of the adjustment so it can be returned if this doesn't help. 1 Quote Link to comment
Jelmer C31 Posted October 9, 2016 Author Report Share Posted October 9, 2016 Can't I just take it of? Quote Link to comment
Jelmer C31 Posted October 9, 2016 Author Report Share Posted October 9, 2016 Forget taking it off! I adjusted it like Mike described and now it doesn't hold revs anymore! Thanks again Mike! Next issue to trace is that during warmup it has a hasitation when in 2nd gear at idle rolling at an intersection and you give gas again. When warmt up the hesitation is gone. Quote Link to comment
datzenmike Posted October 9, 2016 Report Share Posted October 9, 2016 Well the difference is cold vs. warmed up driving. This is the time when the choke is on so, or should be on, so a few checks are in order.... On a cold engine take the top off the air filter and look down. You should see this, below. This is the choke trying to be closed. Work the throttle and it will snap closed... ... like this, below. The closed position forces a rich condition and also engages the fast idle system to speed the warmup. After about 8 min of warm up the choke should be fully open like this, below... Most electric chokes are adjustable to run richer or leaner as needed. Often in very cold weather the choke may need to be adjusted richer so it takes a couple extra minuted longer to warm up. Loosen the three holding screws around the outside and turn counter clockwise to make richer. This one says closed (richer) It should also be noted that when the choke is on or engaged the throttle is held open slightly by a fast idle cam. You should notice the idle much higher than when warmed up. This makes driving easier and speeds the warm up. This is the fast idle cam in the (choke) on position. You can see the under side has steps that the throttle stop closes against to hold it open. As the choke warms up a slowly opens, a linkage rotates the cam out of the way and lowers the idle speed. Quote Link to comment
Jelmer C31 Posted October 9, 2016 Author Report Share Posted October 9, 2016 The choke is working good but the hesitation/hickup is there only when cold. Kind of feels like the acceleration pump doesn't work.(But it works fine on mine) It only does it when taking off. Quote Link to comment
datzenmike Posted October 9, 2016 Report Share Posted October 9, 2016 Cold engines have trouble vaporizing fuel. To help with this a richer mixture is used. Try adjusting your choke towards richer and see if there is improvemnet. Quote Link to comment
Jelmer C31 Posted October 10, 2016 Author Report Share Posted October 10, 2016 One problem solved, a new one arrises! I took it to work today and when warm it has the hesitation now when you step on the gas again after a turn! And when I was at work it idled around 500 rpm.... :confused: Quote Link to comment
banzai510(hainz) Posted October 10, 2016 Report Share Posted October 10, 2016 float issue. carb is old. time the motor. set the valve lash ck the distributor for bushing wear or maybe put another in if you have one. if that dont work then its the carb. Quote Link to comment
datzenmike Posted October 10, 2016 Report Share Posted October 10, 2016 One problem solved, a new one arrises! I took it to work today and when warm it has the hesitation now when you step on the gas again after a turn! And when I was at work it idled around 500 rpm.... :confused: So the problem is solved? Did you turn the choke richer? float issue. carb is old. time the motor. set the valve lash I assumed this was already done before setting the carb idle speed and mixture. Timing has a huge effect on idle quality. Set.check the valve lash also. Then... Idle and idle mixture setting... Warm engine, turn idle down. Turn idle mixture screw in or out. Idle quality may improve and the engine speed up or it may drop off towards stalling. Turn towards the best smooth fast idling You may find there is about one full turn of good idle with a drop off on either side. A sort of plateau. Set in the middle. By now the idle has gone up, so lower it again with the idle speed screw. Repeat the in and out adjustment, set in the middle of the smoothest fastest idle. Repeat as many tines as necessary, all the time seeking the fastest smoothest idle quality, until you can no longer improve it and the idle speed is 750-850. Turn adjustments slow enough that the engine can keep up. Engine idle should improve and become stronger. Always adjust towards improved idle quality. If idle is too high maybe 900 and above these adjustments may have no effect because you are up above the idle setting and in the slow speed circuit. In addition the mechanical and vacuum advance may be engaged making idle adjustments difficult. Quote Link to comment
Jelmer C31 Posted October 10, 2016 Author Report Share Posted October 10, 2016 Well, the weird thing is that it ran perfect when warm yesterday and this morning but this afternoon it started to idle low and the hesitation showed up! Quote Link to comment
datzenmike Posted October 10, 2016 Report Share Posted October 10, 2016 Did you adjust the choke richer? Last thing done is the first place to look when a new symptom shows up. Quote Link to comment
Jelmer C31 Posted October 10, 2016 Author Report Share Posted October 10, 2016 No I did do that yet, planned to do it tonight so that I can test it tomorrow morning when the engine is cold again. Last thing I did was adjust the BCDD. Can this cause a low idle? And the hasitation? Quote Link to comment
datzenmike Posted October 10, 2016 Report Share Posted October 10, 2016 The BCDD shouldn't as it should normally be off at idle. Here's how it works. During high speed deceleration the engine starves for air when the throttle closes and the mixture goes rich. A vacuum sensor in the BCDD opens an air passage through a small 'carburetor within a carburetor' to allow some air and fuel in to adjust this. It acts like a parachute and allows the engine to reduce it's RPMs slower and without being so rich a mixture. When the vacuum reaches a pre set limit the BCDD shuts off. Now if the trigger vacuum settings were out of whack the BCDD may not shut off properly and the added air and fuel will cause a faster idle. If your idle was being set against a BCDD altered idle, it may now be affected by the removal of the BCDD. On a warm engine.... If the BCDD is off, (it normally is) the timing correct, the valve lash checked for clearance, then the idle mixture and speed set it should run normally. If there is poor off idle performance this would likely be the carb then. On a cold engine the choke being on changes everything, idle speed higher, mixture is rich. This can hide a poor idle mixture setting that is evident when warmed up and the choke is off. Quote Link to comment
Jelmer C31 Posted October 10, 2016 Author Report Share Posted October 10, 2016 I drove it again tonight and it idles fine again! I check the timing in a little bit and drive it again. Dizzy cap, leads and plugs are new. Quote Link to comment
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