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Gs750db

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Hello my name is mark and i live in the uk, so last year i went to a bike night and seeing all the old bike the smell and sounds brought it all back and i decided to get a motorbike again after a 25 years and i bought a GS750DB had a 750E in my twenty,s.
Any way i got this DB she,s not running right even tho i had dyna s ignition installed running on 3 cylinders at the mo.
Need to find a good sort as i,m reluctant to go back to the bike shop as i get the impression they dont give a s%*t.

Here are a couple of pics for you to look at as you can see she is clean and looked after should mention she,s an american import 1997 i think.

would i be wasting my time and money gettin dyna coils and leads fitted seeing as i got dyna ignition your thoughts please.



suki 2.jpg
 
Congratulations on the bike acquisition and welcome to the GSR. The ignition coils each fire two cylinders. The one on the left (as you're sitting on the bike) fires 1 and 4 and the one on the right fires 2 and 3. Sitting on the bike, the cylinders are numbered left to right, 1,2,3,4. If you have one cylinder not firing, it is not a coil problem or ignition problem. It is either a spark plug lead, plug cap, wire end or possibly a valve not closing, or a carb blockage problem. Check the plugs and let us know which one is black or wet and not firing and we can go from there.

What is the year and mileage on the bike? Has it been sitting up for an extended time?

Normally, the model designation is followed by the year. i.e GS750EN would be a E model, N=1979. I've never heard of a DB.
 
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Welcome Mark and nice bike!

Check out the plugs as Earl suggests...and thanks Earl for the ignition points.


Ed
 
Hi as far as i know the DB is the twin disc modle 1977 the clocks show 65k cant be sure they are original tho,
i did have the shims done and supposedly the carbs cleaned cant be sure on that either,

a compression test showed 125psi per cylinder which is good,sat on the bike its the 2nd cylinder in from the left thats playing up i do get a spark but not a strong one like the others will check again tomorrow.when i collected the bike they gave me a box with the bits they had removed/changed when i got home and looked inside i knew i made a mistake choosing the shop. sorry about the pic cant see how to rotate it



bits.jpg
 
markla said:
Hi as far as i know the DB is the twin disc modle 1977 the clocks show 65k cant be sure they are original tho,
i did have the shims done and supposedly the carbs cleaned cant be sure on that either,

a compression test showed 125psi per cylinder which is good,sat on the bike its the 2nd cylinder in from the left thats playing up i do get a spark but not a strong one like the others will check again tomorrow.when i collected the bike they gave me a box with the bits they had removed/changed when i got home and looked inside i knew i made a mistake choosing the shop. sorry about the pic cant see how to rotate it



View attachment 54849
Click to expand...

79 and earlier models were made with separate regulator and rectifier. That looks to be the two boxes in your photo along with that wiring removed.
Newer replacement rectifiers are a single, all in one module. A charging rectifier would not be the cause though of a single cylinder not firing well. My first thought for the problem on the #2 cylinder is possibly the spark plug wire end going into the cap is not a good connection. The caps are screw on onto the wire end, Unscrew the cap and check that the strands of wire are splayed so a good connection is made when the cap is re screwed on. Then put a dry spark plug in the cap, ground it to the cylinder head and crank the bike to see if the spark is improved.

If the spark is improved, but the cylinder still will not fire, I would suspect the petcock vacuum line is leaking into the intake. If I remember correctly from my 79 759 E, the vacuum line from the petcock is connected to a fitting on top of the #2 carb. If the petcock leaks internally, vacuum will pull fuel into the cylinder through the leaking vacuum line and flood the cylinder, causing it to not fire. If this is happening, you will likely have a wet or very sooty spark plug. If it is wet and sooty, remove the vacuum line from the petcock (leave the other end on the carb nipple) and plug the petcock end with a pencil or whatever you have. Then turn the petcock to prime and see if the bike will start with a fresh plug in the cylinder. (you can swap the non firing plug to a different cylinder and use the other plug in #2. (so that you know you are starting with a working plug)

After doing the above test, return the petcock to the run position so that fuel will not gravity flow into the float bowls and possibly overfill them when the engine is not running.

Lemme know
 
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@Earlfor, so today i changed spark plugs over and started the bike and number 1 cylinder stayed cold i could,nt believe it a dodgy spark plug,
went through that box of bits chose one of the old plugs put it in and fired her up amazing running on all 4 i was so happy and a little bit annoyed at the shop as they are supposed to be new plugs.

Can not thank you enough Earl been out for a run today all is good again man and machine functioning as one.
tomorrow will be cleaning ,polishing,bleeding the brakes.

it was awsome going on to the motoway soon as i could pulled back on the throttle and away we went still buzzing now.
my bike has got a Yanmar exhaust on it sounds lovley when goiong up through the gears.

heres a pic of the suspect plug which is the top one.
image1.jpg
 
markla said:
@Earlfor, so today i changed spark plugs over and started the bike and number 1 cylinder stayed cold i could,nt believe it a dodgy spark plug,
went through that box of bits chose one of the old plugs put it in and fired her up amazing running on all 4 i was so happy and a little bit annoyed at the shop as they are supposed to be new plugs.

Can not thank you enough Earl been out for a run today all is good again man and machine functioning as one.
tomorrow will be cleaning ,polishing,bleeding the brakes.

it was awsome going on to the motoway soon as i could pulled back on the throttle and away we went still buzzing now.
my bike has got a Yanmar exhaust on it sounds lovley when goiong up through the gears.

heres a pic of the suspect plug which is the top one.
View attachment 54864
Click to expand...

Ouch! spark plugs should not look like the one at the top in the pic. Sheesh! Cheers that you're up and running and it was such a simple deductive logic thing. Gads, I hate shops and mechanics that aren't mechanics. LOL Please, if you have any more problems, post them in the tech sections here and save your money and some frustration. Happy to help and enjoy your ride!

Oh, gaps on the plugs are 28 thousandths. heh
 
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Thanks Earl and will do on posting in the tech section we have a bank holiday tomorrow and ill be making full use of my day off.
think i will be investing in some feeler gauges as well treat suki to a oil and filter change today as i dont know when it was last done i,m slowly finding my way around the bike again carb cleaning and balancing next on the list.

suki.jpg
 
markla said:
Thanks Earl and will do on posting in the tech section we have a bank holiday tomorrow and ill be making full use of my day off.
think i will be investing in some feeler gauges as well treat suki to a oil and filter change today as i dont know when it was last done i,m slowly finding my way around the bike again carb cleaning and balancing next on the list.

View attachment 54865
Click to expand...

Ahhh, something to play with and keep you out of trouble at the same time. What more could you want? LOL Cheers
 
earlfor said:
... If I remember correctly from my 79 759 E, the vacuum line from the petcock is connected to a fitting on top of the #2 carb. ...
Click to expand...
You are CLOSE, Earl. :-k

On the CV-type carbs from '80 onward the vacuum port is on the #2 carb, but on his VM carbs, it's on #3. :encouragement:

.
 
Steve said:
You are CLOSE, Earl. :-k

On the CV-type carbs from '80 onward the vacuum port is on the #2 carb, but on his VM carbs, it's on #3. :encouragement:

.
Click to expand...

It's been 16 years since I sold my 79 750E, so I can live with that. heh
 
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