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1987 Brat Carburetor issues

brat Carburetor Hitachi

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12 replies to this topic

#1 hawksooo

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Posted 23 April 2018 - 12:58 PM

   I'm hoping someone can help me with an issue I am having. I have an 86 brat with the Hitachi Carburetor, I  removed the Carburetor  and cleaned it and installed a rebuild kit (mainly gasket) every since then when it first starts running it'll idle Really high (3-4000 rpms)  then it gets to where it wont idle at all ! another thing it's doing (may or may not be related )  when giving it gas it acts like it's either not getting gas or has a hesitation in it until you rev it up about 25-3000 rpms then it'll open up and take fuel and run like it should. Any advice ? I'm planning on taking the carb back off and tiring it back down but, wanted to hear everyone opinions of what it could be (or what to look for).

 

Thanks  for helping ! 



#2 DaveT

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Posted 23 April 2018 - 01:20 PM

It's been a long time since I did anything with a carb.

1 sounds like choke and or high idle adjustment.

2 sounds like the accelerator pump is not pumping.

Did it run correctly before?

#3 naru

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Posted 23 April 2018 - 01:24 PM

High cold idle is probably a misadjusted fast idle screw.

 

No hot idle could be a lot of things.

 

Bad or unpowered anti diesel solenoid

Flooding(how is the level in the sight glass?)

Misadjusted idle mixture or speed screws

Blocked idle passages

Vacuum leak

etc......


Edited by naru, 23 April 2018 - 01:26 PM.


#4 hawksooo

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Posted 23 April 2018 - 01:43 PM

It's been a long time since I did anything with a carb.

1 sounds like choke and or high idle adjustment.

2 sounds like the accelerator pump is not pumping.

Did it run correctly before?

thanks for the quick reply - like you its been a long while since I've messed with carbs....

the car did run before however the accelerator pump went bad. before it would idle, just fall on it's face with given fuel. 

I did install a new AC pump so I'd think that should had fixed that issue? 

the choke seems to be working (somewhat) but I'll check close before I pull carb off 



#5 hawksooo

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Posted 23 April 2018 - 01:49 PM

High cold idle is probably a misadjusted fast idle screw.

 

No hot idle could be a lot of things.

 

Bad or unpowered anti diesel solenoid

Flooding(how is the level in the sight glass?)

Misadjusted idle mixture or speed screws

Blocked idle passages

Vacuum leak

etc......

thanks for the idea on the anti-diesel solenoid the wire did break on it and I left it unhooked til I got it running right (I thought the only thing the solenoid did was cut fuel to carb when you turned the key off) 

the sight glass is a little over 1/2 fuel of fuel, so maybe a little  high ? 

I also unhooked ALL vacuum from carburetor  and plugged everything off and it  still ran  about the same ? 

I'll be checking everything  ya'll mention before i pull the carb off again !

thanks for the help 



#6 naru

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Posted 23 April 2018 - 01:51 PM

I did install a new AC pump so I'd think that should had fixed that issue? 

 

You tell us.

Look down the carb w/rngine off.Does it squirt fuel w/the throttle is opened?



#7 DaveT

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Posted 23 April 2018 - 04:00 PM

Anti diesel solenoid shuts off fuel at idle. Must be powered open to idle.

Accelerator pump output was a visible squirt / stream of fuel on the carbs I dealt with. It's safest to look with the engine off...., hold the choke open, open the throttle by hand, look down the primary. Be aware of possible splash of fuel.

#8 Subarule

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Posted 23 April 2018 - 11:08 PM

That flat spot after giving it gas is symptomatic of Hitachi carbs. It's some kind of vacuum leak, I'm pretty sure. I had one (a Hitachi) and did everything I could think of to cure it, with no luck. Finally did get the problem solved, by removing the Hitachi and putting a Weber on.

#9 djellum

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Posted 24 April 2018 - 04:24 PM

id check vacuum leaks.  use carb cleaner and spray the base gasket, hoses, and manifold gaskets.  be carefull around the carb and use a straw nozzle if it has one.  you cant spray so much that it gets sucked in the top of the carb.  if theres an idle change theres probably a vacuum leak there.

 

also double check that your linkage isnt too tight and opening the throttle plates to much. 

 

if you can, disable the choke until you get the car to run right.  then adjust it after.

 

check your timing.

 

how did you tune it?  basic way I do it is to disable the choke if possible, wait till its completely warm if not.  hook up a vacuum gauge and use that to tune.  theres online instructions if you want to look them up, but basically looking for highest smooth vaccum setting with the mixture screw.

 

+1 on a weber, best upgrade for them if its legal in your area.



#10 skishop69

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Posted 24 April 2018 - 09:26 PM

It's not a vacuum leak and you have to have all the vacuum lines hooked up for it to run right. I've rebuilt a lot of these Hitachi's, and I've never had one with a flat spot or a vacuum leak that caused this kind of problem. Some of the lines are temp and orifice controlled air bleed circuits for idle and bottom end. If you put them in the wrong place or left them off, you won't get the proper air bleed for the idle and off idle circuits. Also, it's possible to get the jets swapped as well and that will screw you as well. +1 for Dave. The solenoid has to be hooked up and functioning or it will not idle and have a problem on the bottom end.



#11 Gloyale

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Posted 25 April 2018 - 12:17 PM

If you did not pull the emulsion tubes out and clear them that is the problem with the hesitation/flat spot and possibly contributing to the idle issues.

 

The larger "vac" ports are not vacuum thay are the air bleeds for the emulsion tubes.  they need to be hooked up properly.

 

Also the vaccum actuator for the secondaries should be hooked up too.  Might want the distributor vac advacne too.

 

I do not get why some people think "unhooking all vac lines" is ever a fix.  Understand what something does before you throw it out OK?



#12 hawksooo

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Posted 02 May 2018 - 07:57 PM

ok sorry it's taken me so long to get back on the brat issue... Thanks for all the advice , I do welcome all ideas ,even if what I done was wrong as Gloyale mentioned  :D  ... 

I am going to get back working on the brat soon (hopefully tomorrow) and I'lll get back on here and let you all know whats' up ! 
I do have a question , skishop69 , you said the jets could be switched ( although I dont think so ) but if  they were do you know what issue's it may cause ? 

 

I did check the Accelerator pump and for some reason it's not squirting as it should. Its more like a trickle and not a squirt, the AC pump is new ? any ideas on what could cause that ? 

 

again thanks for all the previous & future advice  !  

 

P.S. if anyone is in NC and would like to take on a challenge , I wouldn't oppose it  LMAO 



#13 skishop69

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Posted 02 May 2018 - 08:31 PM

Swapping the jets would result in similar issues to what you're having. Smaller number main and air bleed jets go in the primary circuit, larger number in the secondary. Only a few things can cause the AC pump to trickle. Worn pump, but you replaced it. No check ball in the bottom of the well, or the wrong size ball and an obstructed passage. this could be something physically lodged in the passage or the gasket is wrong or cut wrong.







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