1989-90 Suzuki GSXR 400R SP Issues

**Hainswof** · 13th April 2007, 01:17

Hey there people,

I'm recently new to this forum, so Hi to everyone.

Just wanted to pick your brains in regards to a couple of issues i am having with my recently purchase GSXR.

Mods done by previous owner:
Airbox - This has been modified from stock. It appears to have both the two large chambers heading toward the front of the bike cut off. One of the two holes into the airbox has been covered/blocked off, and the other has a pipe attached to it with a K & N Filter fastened on the end.

Issues:

1. The first, and most annoying issue, is an engine "bogging" fault. When opening the throttle fully from anywhere lower than about 7,000 RPM, the engine will sound like its grumbling/missing and will stay at around 5,000RPM and not rise any higher. However, when opening the throttle 0-60%ish i can get it past 7,000RPM and then use full throttle. It will then rev up to redline no worries. I will also miss slightly when riding above 7,000RPM and is noticable mostly in the 4th or 5th gears under acceleration. Spark plugs seem to be OK.

2. The other issue i am having is when riding, whether crusing or accelerating, my entire lighting system (headlights, speedo light etc) will continuously dimm, then brighten and so on. This makes it very frustrating riding at night.

Any help with these issues will be most appreciated.

Thanks,
Chris.

**sugilite:Me** · 13th April 2007, 08:18

I think it is safe to say that issue one is connected directly to the air box mods. I'd restore the air box back to standard as possible (inc the air filter if the K and N does not look like it is designed for your model) and check that the jetting in the carbs is standard (I suspect it is judging from the way they blocked holes of etc)

Issue 2 sounds like the battery may not be charging off the motor as it should be.

Good luck with that.

**El Dopa** · 13th April 2007, 19:40

Originally Posted by Hainswof

Hey there people,

I'm recently new to this forum, so Hi to everyone.

Just wanted to pick your brains in regards to a couple of issues i am having with my recently purchase GSXR.

Mods done by previous owner:
Airbox - This has been modified from stock. It appears to have both the two large chambers heading toward the front of the bike cut off. One of the two holes into the airbox has been covered/blocked off, and the other has a pipe attached to it with a K & N Filter fastened on the end.

Issues:

1. The first, and most annoying issue, is an engine "bogging" fault. When opening the throttle fully from anywhere lower than about 7,000 RPM, the engine will sound like its grumbling/missing and will stay at around 5,000RPM and not rise any higher. However, when opening the throttle 0-60%ish i can get it past 7,000RPM and then use full throttle. It will then rev up to redline no worries. I will also miss slightly when riding above 7,000RPM and is noticable mostly in the 4th or 5th gears under acceleration. Spark plugs seem to be OK.

2. The other issue i am having is when riding, whether crusing or accelerating, my entire lighting system (headlights, speedo light etc) will continuously dimm, then brighten and so on. This makes it very frustrating riding at night.

Any help with these issues will be most appreciated.

Thanks,
Chris.

1) Put the airbox back to standard. If you want to muck around with it later on, and try to get better flow, drill holes in the plastic above the filter. Then it's easy to tape them up if it doesn't have the desired effect.

2) Could very possibly be a faulty reg/rec.

**Hainswof** · 14th April 2007, 00:20

Thanks guys,

I'll have another look tomorrow. You don't happen to know where i could purchase a standard airbox do you? It's proving very difficult to find one.

Thanks,
Chris.

**QMOTO** · 14th April 2007, 15:15

Airbox, no question, I had a gsxr400 sp race bike and had a few dramas very similiar to yours, you need to get it back to original, there is a website UK based where you can find some info, and or a new airbox.
http://www.400greybike.co.uk/Forum/default.asp?CAT_ID=7

There is a member here named SLIM, her partner Craig will have a box somewhere as he has taken his out and is using a external filter system, good luck finding him, he races at most F3 events, I will keep an eye out for him also

In the meantime tape up the box to seal of the extra holes, and look at getting it dyno tuned again.

Good luck

**El Dopa** · 14th April 2007, 15:41

Or try:

http://www.gsxr400.co.uk/

For tracing your electrical problem - try this:

http://www.electrosport.com/electros...t_finding.html

**bumsex** · 17th April 2007, 20:13

I would check your electrical eaths before getting into things like the reg/rec.

you could probaly get your bike to run fine as it is with some carb fettling. try raising the needles one notch and see what that does to your bogging problem

**Hainswof** · 18th April 2007, 12:38

Yeah, i have adjusted the needles up one notch in my attempt to fix, however it didn't fix the bogging. It did however bring the idle up to a nicer RPM.

I am in the process of sourcing an airbox, however, having difficulties.

I wonder if the missing at the top of the rev range has to do with the ignition box or CDI i think they are called. I hear they are notorious for failing. I could be VERY wrong though.

**Hainswof** · 18th April 2007, 12:42

Originally Posted by QUASiMOTO

In the meantime tape up the box to seal of the extra holes, and look at getting it dyno tuned again.

Good luck

Should this "modified" airbox make the bike perform better if dyno tuned and sealed properly?

Thanks,
Chris.

**bumsex** · 18th April 2007, 17:57

then you should strip the carbs and play with the needle and emulsion tube sizes. try raising the needles again before you do this though

**El Dopa** · 18th April 2007, 18:28

Originally Posted by Hainswof

I wonder if the missing at the top of the rev range has to do with the ignition box or CDI i think they are called. I hear they are notorious for failing. I could be VERY wrong though.

My understanding of the CDI failing is that you usually won't get any spark at all if the unit has failed.

Its possible (but I don't think likely) that the solder joints in the CDI could have dried out and cracked, so the signal was intermittent, but this would mean more or less random surging in the revs, not always at the same point.

EDIT: There's a gsxr400 CDI unit for sale REALLY cheap on trademe at the moment. If this fits your bike, it might be worth buying as a spare.

**Hainswof** · 19th April 2007, 02:47

Originally Posted by El Dopa

EDIT: There's a gsxr400 CDI unit for sale REALLY cheap on trademe at the moment. If this fits your bike, it might be worth buying as a spare.

http://www.trademe.co.nz/Browse/List...px?id=96021275
Is there a difference between the standard 400 and SP 400 CDI units?

**El Dopa** · 19th April 2007, 19:30

Originally Posted by Hainswof

http://www.trademe.co.nz/Browse/List...px?id=96021275
Is there a difference between the standard 400 and SP 400 CDI units?

Erm.....Ask me another?

You'll have to ask around on either banditalley.com (have a look in the 400 part of the forum, or PM gsxr400racer), or possibly someone on gsxr400.com will know.